Glossary

What a word means, in two sentences. This page is a reference, not a lesson: no steps, no choices, just the definition and where the site uses it.

277 terms, in 12 groups.

Thinking and problem solving

The words for how a solution is planned before any code exists.

Step count(operation count): Counting the work an algorithm does by counting the operations it runs. A loop over n items costs n steps, and a loop inside a loop costs n times n. The count is what predicts slowness before any timer runs.; See also: Computational complexity

See also: Loop

Used in: Measuring Work
Growth rate(how the cost grows): The shape a step count takes as the input gets bigger, ignoring the constant in front. One pass is linear, a pass inside a pass is quadratic, halving each step is logarithmic. The shape is what tells you which algorithm to pick.; See also: Computational complexity

See also: Step count

Used in: Measuring Work
Best case: The cheapest an algorithm can be on the easiest input. A search that finds the item on the first try has a best case of one step. Best case alone says little, so it is always reported with the others.; See also: Computational complexity

See also: Worst case

Used in: Measuring Work
Worst case: The most work an algorithm can take on the hardest input of a given size. This is the number to plan with, since a real user can hit the hard input. A guarantee on the worst case is stronger than an average.; See also: Computational complexity

See also: Best case

See also: Average case

Used in: Measuring Work
Average case(expected cost): The work an algorithm takes over typical inputs rather than the hardest one. It needs an assumption about what typical means, so it is a weaker claim than a worst case bound. Quicksort is a common example.; See also: Computational complexity

See also: Worst case

See also: Quicksort

Used in: Measuring Work
Space complexity(memory cost): How much memory an algorithm holds at its peak as the input grows. A running total is constant, a copy of the input is linear, a grid is quadratic. Peak matters, not the total ever allocated.; See also: Computational complexity

See also: Stack

See also: Call stack

Used in: Measuring Work
Lower bound(floor): A proven minimum cost that no algorithm can beat for a problem. Finding the largest item needs a look at every item, so n is its floor. When your cost matches the floor, the algorithm is optimal and tuning further is wasted effort.; See also: Computational complexity

See also: Binary search

Used in: Measuring Work
Amortized cost(amortized analysis): The cost of an operation averaged over a long run, where an occasional expensive step is spread across many cheap ones. Growing a list is cheap most times and costly when it copies, and the average per add stays constant.; See also: Computational complexity

See also: Array

Used in: Measuring Work
Logarithm(log n): How many times a number can be halved before it reaches one. A million halves about twenty times, so a search that halves the range each step costs about twenty steps at any large size. Halving is where logarithmic cost comes from.; See also: Computational complexity

See also: Binary search

Used in: Measuring Work
Optimal algorithm(optimal): An algorithm whose cost matches a proven floor for the problem. A linear scan that must read every item cannot be improved in class. Recognising optimal stops you from wasting effort on tuning the wrong thing.; See also: Computational complexity

See also: Lower bound

Used in: Measuring Work
Algorithm: A finished recipe of steps that solves a problem. Pseudocode, a flowchart, and a working program are all the same algorithm written in different notations.; See also: Pseudocode

See also: Flowchart

See also: Decomposition

Used in: Logic & Problem Solving
Decomposition: Splitting one big problem into smaller problems that can be solved and tested on their own. Each piece gets its own function, and the pieces are joined by a small amount of glue code.; See also: Abstraction

See also: Algorithm

Used in: Logic & Problem Solving
Abstraction: Naming what a solution does and hiding how it does it, so a reader can reason about the parts instead of the details. A function name is an abstraction over its body.; See also: Decomposition

See also: Function

Used in: Logic & Problem Solving
Pseudocode: Plan-shaped English that uses programming words like `if`, `while`, and `return` but no real syntax. It is written to be read once and then replaced by code.; See also: Algorithm

See also: Flowchart

Used in: Logic & Problem Solving
Flowchart: A diagram of a plan: boxes for steps, diamonds for decisions, arrows for what comes next. It carries the same meaning as pseudocode, in a shape a reader can follow with a finger.; See also: Pseudocode

See also: Conditional

Used in: Logic & Problem Solving
Edge case: An input at the boundary where a solution can behave differently: an empty list, a single item, a zero, a negative, the last index. Testing these finds bugs that middle-of-the-road inputs hide.; See also: Invariant

See also: Regression

Used in: Logic & Problem Solving
Invariant: A statement about a program that stays true the whole way through, even inside a loop. Naming it makes a loop provably correct: "everything before `i` is sorted" tells you when the loop may stop.; See also: Loop

See also: Edge case

Used in: Logic & Problem Solving
Off-by-one error(fencepost error): A count that is one too many or one too few, usually at the first or last item. The classic cause is mixing a length with a last index: an array of 5 items has indexes 0 to 4.; See also: Index

See also: Edge case

Used in: Logic & Problem Solving

Used in: Data Structure Basics
Debugging: Finding why a program gives the wrong answer by testing small parts and reading what actually happened, rather than by rereading the whole file. Print the value you expected and the value you got, at the point where they disagree.; See also: Regression

See also: Edge case

Used in: Logic & Problem Solving
Regression(regression test): A change that broke something that used to work. A test that used to pass and now fails is a regression, and it is fixed before any new feature is added on top.; See also: Debugging

See also: Code review

Used in: Logic & Problem Solving
Computational complexity(Big-O): How the work a program does grows as the input grows. O(n) means one pass, O(n squared) means a pass inside a pass, O(log n) means halving the search each step. It predicts slowness before a timer is needed.; See also: Hash map

See also: Index

Used in: Data Structure Basics

Data and structures

The shapes information is put into, and what each one is good at.

Stream(streaming): Data that is processed a piece at a time as it arrives, so the whole thing never has to be held in memory at once.; See also: Buffer

See also: Byte

Used in: Text & Files
Buffer(chunk): A block of bytes read or written at one time, sized to what the device handles fastest rather than to the whole file.; See also: Byte

Used in: Text & Files
Delimiter(separator): The character that marks where one field ends and the next begins in a line of text.; See also: CSV

Used in: Text & Files
Newline(line ending): The one or two characters that end a line of text, stored in the file rather than added by the reader.; See also: Delimiter

Used in: Text & Files
File extension(suffix): The characters after the last dot in a name, used by tools to guess what kind of file it is.; See also: Path

Used in: Text & Files
Directory(folder): A file whose contents are a list of other names, which is how a tree of files is stored.; See also: Path

See also: File extension

Used in: Text & Files
UTF-8(utf8): The encoding that maps every symbol to one to four bytes, and the safe default to name on every file.; See also: Encoding

See also: Code point

Used in: Text & Files
Truncation(truncated): A file left shorter than it should be because a write stopped partway, which a reader sees as a partial record.; See also: Stream

Used in: Text & Files
Atomic write(atomic replace): Saving a new version to a temporary name and renaming it into place, so a reader never sees half a file.; See also: Truncation

See also: Directory

Used in: Text & Files
Sort: Put a row of items into order by a chosen rule, so that every item is no greater than the one after it. Ordering is what makes fast searching and grouping possible.; See also: Merge sort

See also: Quicksort

See also: Stable sort

Used in: Sorting & Searching
Search: Look for an item in a row. On an unsorted row you check one by one; on a sorted row you can cut the row in half each look.; See also: Binary search

Used in: Sorting & Searching
Binary search: Find a value in a sorted row by checking the middle and keeping only the half that can hold it. Each look halves the row, so a million items take about twenty looks.; See also: Search

See also: Sort

Used in: Sorting & Searching
Merge sort: A fast sort that splits the row in half, sorts each half, then merges the two ordered halves. It keeps ties in order and costs about n log n.; See also: Sort

See also: Stable sort

Used in: Sorting & Searching
Quicksort: A fast sort that picks a pivot, puts smaller items left and bigger right, then sorts each side. Usually quick, but a bad pivot makes it slow.; See also: Sort

See also: Merge sort

Used in: Sorting & Searching
Stable sort: A sort that keeps equal items in the order they started. Stability is what lets you sort by several fields one at a time.; See also: Sort

See also: Merge sort

Used in: Sorting & Searching
Bit: The smallest unit of information: one switch with two positions, read as 0 or 1. A machine is built from bits, and every value it stores is a row of them.; See also: Byte

Used in: Binary & Data Representation
Byte: A row of eight bits, the smallest piece of memory a machine can point at on its own. A byte holds 256 values, and file and memory sizes are counted in bytes.; See also: Bit

See also: Hexadecimal

Used in: Binary & Data Representation
Binary number: A value written in base two, where each position is worth double the one to its right. A number is the sum of the powers of two that are switched on.; See also: Bit

See also: Integer

Used in: Binary & Data Representation
Hexadecimal: A sixteen-digit shorthand for bits where each digit is exactly four bits, so a byte is always two hex digits. Colors, byte dumps, and hashes are written this way.; See also: Bit

See also: Byte

Used in: Binary & Data Representation
Twos complement: The standard way to store negative numbers in a fixed row of bits, where the top bit marks the sign and flipping the bits then adding one gives the negative. It lets a number and its negative add to zero with no special case.; See also: Integer

See also: Binary number

Used in: Binary & Data Representation
Signed number: A fixed-width integer read as able to go negative, using twos complement. The same bytes read unsigned give a different number, so the signed flag is a reading choice.; See also: Twos complement

See also: Overflow

Used in: Binary & Data Representation
Overflow: What happens when a value is too big for its fixed width: the count wraps to the bottom with no error. A byte counter at 255 plus one reads as zero, which is a silent wrong number.; See also: Integer

See also: Signed number

Used in: Binary & Data Representation
Endianness: The order a multi-byte number is written in, big end first or little end first. The same bytes read in the other order give a wrong number, which is why formats state their byte order.; See also: Byte

Used in: Binary & Data Representation
Integer(whole number, int): A value with no fractional part. Whole numbers are stored exactly and their arithmetic is exact, which is why counts and money in cents are kept as integers rather than decimals.; See also: Float

See also: Type

Used in: Values & Variables

Used in: Python
Float(decimal, floating point): A value that can hold a fractional part, stored as a binary fraction with a fixed number of bits. That fixed width means some decimals, like a tenth, are rounded to the nearest value the bits can hold.; See also: Integer

See also: Rounding error

Used in: Values & Variables
Rounding error: The small gap between a decimal value and the nearest one the machine can actually store. It is why a sum of decimals can print 0.30000000000000004, and why decimals are compared by closeness rather than exact equality.; See also: Float

See also: Integer

Used in: Values & Variables
Code point: The number a single character is given in a character set. Text is a list of code points, which is why a character can be measured, indexed, and compared at all.; See also: Encoding

See also: String

Used in: Values & Variables

Used in: Binary & Data Representation
Encoding: The rule that maps bytes to code points and back. Two tools that disagree about the rule turn the same bytes into different text, which is the cause of garbled characters.; See also: Code point

See also: String

Used in: Values & Variables

Used in: Binary & Data Representation
Array(list): An ordered row of values with fixed positions, read by number. Reading any position is fast; inserting in the middle moves everything after it.; See also: Linked list

See also: Index

See also: Stack

Used in: Data Structure Basics
Linked list: A chain of nodes that each point at the next. Adding at the front is instant, but reaching the middle means walking from the front one node at a time.; See also: Array

See also: Pointer

Used in: Data Structure Basics
Stack: A last-in, first-out pile: you push an item and pop the one on top. Function calls use one implicitly, which is why recursion has a depth limit.; See also: Queue

See also: Recursion

Used in: Data Structure Basics
Queue: A first-in, first-out line: items join at the back and leave from the front. Breadth-first search and fair scheduling both need this order rather than a stack's.; See also: Stack

See also: Graph

Used in: Data Structure Basics
Hash map(dictionary, map): A set of key and value pairs where the key is turned into a number, so looking one up costs about the same work no matter how many pairs are stored. The go-to answer for "have I seen this before".; See also: Set

See also: Computational complexity

Used in: Data Structure Basics
Set: A collection of distinct values with no order, used for membership tests: is this already in? Adding a duplicate changes nothing, which makes it a natural way to remove duplicates.; See also: Hash map

Used in: Data Structure Basics
Tree: A structure where each node has children and no cycles, so there is exactly one path from the root to any node. A folder layout, a DOM, and a decision tree are all trees.; See also: Graph

See also: Recursion

Used in: Data Structure Basics
Graph: Nodes joined by edges, where a node may have many paths to another and cycles are allowed. Anything with "can you get from A to B" is a graph question.; See also: Tree

See also: Queue

Used in: Data Structure Basics
Index: The position number of an item in an ordered collection. The first item is index 0, so the last is length minus one.; See also: Off-by-one error

See also: Array

Used in: Data Structure Basics

Used in: Python
Mutation: Changing a value that is already stored, rather than making a new one. A function that mutates its input surprises every other caller that holds the same value.; See also: Reference

Used in: Data Structure Basics
Reference: A name that points at a value stored elsewhere instead of holding a copy. Two references to the same list mean one list, so changing it through either name changes it through both.; See also: Mutation

Used in: JavaScript

Used in: Python
Pointer: A raw memory address held in a variable, as Rust and C use it. Owning and borrowing rules exist to make sure a pointer never points at memory that has been freed.; See also: Reference

Used in: Rust
Recursion: A function that calls itself on a smaller piece of the problem, with a case that stops. A tree is walked recursively because each branch is a smaller tree.; See also: Stack

See also: Tree

Used in: Logic & Problem Solving

Used in: Data Structure Basics

Languages and syntax

Words that mean different things in different languages, and why they differ.

Pattern(regular expression, regex): A short text that describes a set of strings instead of one string. The characters that mean themselves are mixed with characters that mean rules, which is why a pattern needs its own reading.; See also: Metacharacter

See also: Quantifier

Used in: Text Patterns
Metacharacter(special character): A character in a pattern that carries a rule instead of meaning itself. A dot matches any character and a bracket opens a set, so text from a stranger has to be escaped before it becomes a pattern.; See also: Pattern

See also: Escape

Used in: Text Patterns
Character class(character set, bracket expression): A bracketed list of the characters allowed at one position. A dash inside the brackets means a range, and a caret first means everything except the list.; See also: Metacharacter

Used in: Text Patterns
Quantifier(repetition operator): A mark after a piece of a pattern saying how many times it may repeat. A star means none or more and a plus means one or more, so the piece can vanish or stretch.; See also: Greedy match

Used in: Text Patterns
Anchor(zero width assertion): A mark that tests a position rather than consuming a character. A caret asks for the start of a line and a word edge asks for a boundary, so nothing is eaten and nothing moves.; See also: Quantifier

Used in: Text Patterns
Alternation(pipe, either or): A vertical bar in a pattern offering more than one way to fit. The branches are tried in the order written, so the first one that fits wins even when a later one is longer.; See also: Backtracking

Used in: Text Patterns
Capture group(parenthesised group): A pair of brackets in a pattern that remembers which text fit inside it, so a field can be read out of a match instead of slicing offsets by hand.; See also: Pattern

Used in: Text Patterns
Greedy match(greedy quantifier): A quantifier that takes as many characters as it can before checking the rest of the pattern. It gives the longest fit, and it backtracks when the rest of the rule then fails.; See also: Quantifier

See also: Backtracking

Used in: Text Patterns
Lazy match(non-greedy quantifier, reluctant quantifier): A quantifier with a question mark after it that takes as few characters as it can. It stops at the first fit, which is what a pair of tags needs to avoid swallowing the text between them.; See also: Greedy match

Used in: Text Patterns
Base case(stopping case): The branch of a recursive function that answers without calling itself. Without one, the calls never stop and the stack runs out of room.; See also: Recursion

See also: Tree

See also: Loop

Used in: Recursion
Memoization(caching calls): Keep each answer a recursive function already computed in a cache, so a repeated call returns the stored value instead of recomputing the same tree.; See also: Recursion

See also: Sort

Used in: Recursion
Divide and conquer: Split a problem into smaller independent parts, solve each the same way, then combine the answers. The split sets the depth, so halving gives a shallow tree.; See also: Recursion

See also: Sort

See also: Search

Used in: Recursion

Used in: Sorting & Searching
Backtracking: Try one choice, recurse, and undo it when the choice leads to a dead end. The undo step is what lets the search explore every option.; See also: Recursion

See also: Loop

Used in: Recursion
Tail recursion: A recursive call that is the last thing a function does, with nothing left to combine after it returns. A loop can replace it, so the stack stays constant.; See also: Recursion

See also: Loop

Used in: Recursion
Dynamic programming: Solve a problem by writing it as a recurrence over smaller states and storing each state once, either top-down with a cache or bottom-up by filling a table.; See also: Recursion

See also: Memoization

Used in: Recursion
Stack overflow: Running out of room on the call stack, usually from recursion that nests deeper than the limit. The fix is a base case, a loop, or your own stack in memory.; See also: Stack

See also: Recursion

Used in: Recursion
Signature: The first line of a function: its name and the parameters it needs. Reading a signature tells a caller what to pass in and what comes back, without opening the body.; See also: Function

See also: Parameter

Used in: Functions & Abstraction

Used in: Python
Docstring: The sentence written at the top of a function that states what it returns and how it handles the edge cases. It is the contract a caller reads instead of guessing.; See also: Function

See also: Signature

Used in: Functions & Abstraction

Used in: Python
Call stack: The record of which function is running inside which. Each call adds a layer, and a function that calls itself without an end fills the stack with no room left.; See also: Function

See also: Recursion

See also: Scope

Used in: Functions & Abstraction
Default(default argument): The value a parameter uses when the caller leaves it out. A default records the normal case, so a call only supplies what is different.; See also: Parameter

See also: Function

Used in: Functions & Abstraction

Used in: Python
Unpacking: Splitting a returned tuple or list into separate names in one line, so low, high = pair. The number of names has to match the number of parts.; See also: Return value

See also: Function

Used in: Functions & Abstraction

Used in: Python
Expression: A piece of code that works out to a single value. An expression can sit wherever a value is allowed, which is what lets a calculation go inside a print or an assignment.; See also: Assignment

See also: Type

Used in: Values & Variables

Used in: Python
Precedence: The order in which the parts of an expression are worked out, so that multiply happens before add. Parentheses override it, and using them is clearer than remembering the rules.; See also: Expression

See also: Type

Used in: Values & Variables
Literal: A value written directly in the code, like 42 or "owl". A literal is a value with no name, the simplest thing a name can be assigned to.; See also: Type

See also: Expression

Used in: Values & Variables
Conversion(cast): Turning a value from one type into another on purpose, like turning text read from input into a number. Doing it explicitly is what keeps a program from guessing the wrong kind.; See also: Type

See also: Coercion

Used in: Values & Variables

Used in: Python
String(text): A value that is a run of characters, written in quotes. Text is measured and indexed by position, not by meaning, which is why trimming and slicing work on any input.; See also: Type

See also: Concatenation

See also: Code point

Used in: Values & Variables

Used in: Python

Used in: JavaScript
Concatenation: Joining two strings end to end to make a new one. Joining is different from adding numbers, and mixing the two by accident is the classic type error.; See also: String

See also: Type

Used in: Values & Variables

Used in: Python
None(null, nil): A single value that means nothing has been chosen yet. It is what a name holds before it gets a real value, and the honest way to record that a search found nothing.; See also: Type

See also: Variable

Used in: Values & Variables

Used in: Python
Scope: The part of a program where a name can be seen. A name made inside a function belongs only to that function, so two functions can each use the same short name without colliding.; See also: Variable

See also: Function

Used in: Values & Variables

Used in: Python

Used in: JavaScript
Variable: A name that holds one value at a time. The name is for the reader; the value is what the program uses. A name like `d` says nothing, a name like `secondsLeft` says the truth.; See also: Type

See also: Assignment

Used in: Python

Used in: JavaScript
Assignment: Putting a value into a name, read right to left: the expression on the right is computed first, then stored under the name on the left. It is not a claim of equality.; See also: Variable

Used in: Python
Type: What kind of value a name holds: a number, a string, a boolean, a list of things. Strong typing means the computer refuses to mix kinds without an explicit conversion.; See also: Static typing

See also: Coercion

Used in: Python

Used in: TypeScript
Static typing: Checking the kinds of values before the program runs, so a mistake is a build error rather than a surprise at three in the morning. TypeScript and Rust do this; Python checks at runtime instead.; See also: Type

See also: Coercion

Used in: TypeScript

Used in: Rust
Coercion: A language quietly changing one type into another, like treating a number as a string. It is the cause of many baffling bugs, which is why explicit conversion is preferred.; See also: Type

See also: Static typing

Used in: JavaScript
Function: A named block of steps that takes inputs and gives back one result. Calling it runs the block; writing its name without brackets hands the block itself to something else.; See also: Parameter

See also: Return value

See also: Pure function

Used in: Python

Used in: JavaScript
Parameter(argument): A parameter is the name a function declares it needs; an argument is the actual value a caller passes into that name. The two words name the same slot from two sides.; See also: Function

See also: Return value

Used in: Python
Return value: The single result a function gives back. A function with no `return` still returns something in most languages, usually a null-like value, which is why a missing return is a silent bug.; See also: Function

See also: Side effect

Used in: Python

Used in: JavaScript
Side effect: A function that changes something outside itself: writes a file, updates a global, prints, mutates a shared list. A function with no side effects is called pure, and pure functions are the ones that are easy to test.; See also: Pure function

See also: Mutation

Used in: Python
Pure function: A function whose result depends only on its inputs and that changes nothing else. Same input always gives the same output, so it can be tested, cached, and reordered safely.; See also: Side effect

See also: Function

Used in: Python
Conditional: A branch: if this is true do this, otherwise do that. The condition is an expression that must evaluate to a boolean, not a value that is merely truthy or falsy.; See also: Boolean

See also: Flowchart

Used in: Logic & Problem Solving

Used in: Python
Boolean: A value that is one of two: true or false. Every condition must reduce to one of these, even when it is written as a longer expression.; See also: Conditional

See also: Coercion

Used in: Logic & Problem Solving
Loop: Steps that repeat until a condition becomes false. A loop that never ends, or ends one step early, is the most common bug in a first program.; See also: Invariant

See also: Iteration

See also: Off-by-one error

Used in: Logic & Problem Solving
Iteration: Going over a collection one item at a time, without counting indexes yourself. `for item in items` is iteration; `for i in range(len(items))` is counting, and is usually the wrong shape.; See also: Loop

See also: Index

Used in: Python
Compiler: A program that turns source code into a form a machine runs, before the program starts. Errors are caught before anything runs, which is why typed compiled languages fail at build time.; See also: Interpreter

See also: Static typing

Used in: Rust

Used in: Go
Interpreter: A program that reads and runs source one statement at a time. Mistypes and wrong types are found while running, which is why a Python error can appear only on the branch that was taken.; See also: Compiler

See also: Runtime

Used in: Python

Used in: JavaScript
Runtime: The engine that runs a program, and the time it takes while running. "Runtime error" means the program started and then failed, as opposed to a build error that stops it starting.; See also: Interpreter

See also: Compiler

Used in: Python

Used in: JavaScript
Standard library: The set of tools a language ships with, already installed and already tested. Reaching for it before writing your own version is the difference between a working program and a reinvented one.; See also: Package manager

See also: Module

Used in: Python

Used in: Go
Module: A file of code that other files can import by name. A module should do one thing, so its name describes the thing and its imports describe the need.; See also: Package manager

See also: Standard library

Used in: Python

Used in: JavaScript
Package manager: The tool that installs and versions third-party code: npm for JavaScript, pip for Python, cargo for Rust. It also records what versions a project depends on, which is how a build is reproducible.; See also: Module

See also: Semantic versioning

Used in: JavaScript

Used in: Rust
Class: A type with named fields and methods, used when several values always travel together. A game player, a request, and a parsed config are all worth a class; a pair of numbers is not.; See also: Object

See also: Module

Used in: Java

Used in: TypeScript
Object: A value with named fields rather than numbered positions. In JavaScript it is also the shape most JSON and API responses come in.; See also: Class

See also: JSON

Used in: JavaScript

Used in: TypeScript

Web and apps

The parts of a running web application, named so a reader can find the right file.

DOM: The document object model: the browser's live tree of elements built from the HTML. It is a tree, which is why walking it uses the same shape as walking any other tree.; See also: Tree

See also: Render

Used in: JavaScript
Route: A URL path a server answers, and the handler that answers it. Express matches routes in the order they are mounted, which is why mount order changes behaviour.; See also: Endpoint

See also: Middleware

Used in: Full-Stack Web App

Used in: JavaScript
Middleware: A function that runs before every route handler: security headers, language, cache control. Order matters, and a middleware that forgets to call `next()` stops the request silently.; See also: Route

Used in: Full-Stack Web App
Endpoint: One URL and method an API offers, with a documented shape in and a documented shape out. A client and a server agree only when both describe the same endpoint.; See also: Route

See also: JSON

Used in: Full-Stack Web App
JSON: JavaScript object notation: the text format data travels as over a wire. It has no comments and no trailing commas, which is why a config file written as JSON cannot be annotated.; See also: Object

See also: Endpoint

Used in: Full-Stack Web App
HTTP status code: The number a response carries: 200 means it worked, 300s mean "go somewhere else", 400s mean the request was wrong, 500s mean the server broke. A browser console shows this number first for a reason.; See also: Endpoint

See also: Redirect

Used in: Full-Stack Web App
Redirect: A response that sends the reader to another URL instead of a page. 301 says the old address is gone for good, 302 says it may move back, which is what a crawler uses to decide.; See also: HTTP status code

Used in: Full-Stack Web App
Cache header: Instructions a response carries about how long it may be reused: `max-age=300` means five minutes, `no-store` means never. A stale page after a change is almost always a cache header plus a version token.; See also: Cache busting

See also: HTTP status code

Used in: Full-Stack Web App
Cache busting: Changing the URL of a file when its content changes, by adding a version token like `?v=20261010`. A new URL is a new file to a cache, so the new CSS is served the moment it is published.; See also: Cache header

Used in: Full-Stack Web App
Session cookie: A small value the browser keeps so the server can recognise the same visitor again. It is the only state a browser has, which is why "stay signed in" is a cookie question.; See also: Session

See also: Authentication

Used in: Full-Stack Web App
Session: One visit, seen as one identity by the server. Everything that belongs to "this person right now" (who they are, what they ticked, what they are reading) hangs off the session, and signing out or rotating a secret ends it.; See also: Session cookie

See also: Secret

Used in: Full-Stack Web App
Authentication: Proving who a request is from. The password is never stored, only a hash, so a leaked database cannot hand over someone password.; See also: Authorization

See also: bcrypt

See also: Session cookie

Used in: Full-Stack Web App
Authorization: Deciding what a signed-in person may do. Authentication answers "who", authorization answers "is this allowed", and a page that confuses the two has a security hole.; See also: Authentication

Used in: Full-Stack Web App
bcrypt: A deliberately slow hash with a random salt, made for passwords. Slow is the point: an attacker with a stolen database cannot try billions of guesses cheaply.; See also: Hash

See also: Salt

See also: Authentication

Used in: Full-Stack Web App
Salt: Random bytes mixed into a value before hashing, so two users with the same password get different hashes. Without it, one lookup table cracks every password.; See also: Hash

See also: bcrypt

Used in: Full-Stack Web App
Hash: A one-way fingerprint of a value: same input always gives the same output, and the input cannot be recovered from the output. Hashing is for comparing and detecting, never for reading back.; See also: Salt

See also: bcrypt

See also: Hash map

Used in: Full-Stack Web App

Used in: Data Structure Basics
SQLite: One database file and one process, with no server to run. It is the whole reason a small app can have real storage without a server.; See also: Write-ahead log

See also: Database

Used in: Full-Stack Web App
Database: A store of records you query instead of holding in memory. A table is a set of rows with named columns, and a query describes the rows you want.; See also: SQLite

See also: Query

Used in: Full-Stack Web App
Query: A description of the rows you want, run by the database instead of a loop in your code. A prepared query is compiled once and reused with different values.; See also: Database

See also: SQLite

Used in: Full-Stack Web App
Write-ahead log: A database journal where writes go first, so a crash cannot lose an acknowledged write. It explains sidecar files next to a database file, and why they must be deleted together.; See also: SQLite

See also: Transaction

Used in: Full-Stack Web App
Transaction: A group of writes that either all happen or none do. Anything that must stay consistent across two tables belongs in one transaction, not in two separate writes.; See also: Write-ahead log

See also: Race condition

Used in: Full-Stack Web App
Race condition: A result that depends on which of two things finished first. Two requests writing the same counter at once is a race, and it is why a shared counter needs a transaction.; See also: Transaction

Used in: Full-Stack Web App
Environment variable: A value the operating system hands a process at start, used for secrets and settings that must not live in the code. A secret committed to a repository is a secret in public.; See also: Secret

Used in: Full-Stack Web App
Secret: A value that must stay unknown to readers of the code, like a signing key. Rotating a secret invalidates the tokens made with the old one, which signs everyone out.; See also: Environment variable

See also: Session

Used in: Full-Stack Web App
Content Security Policy: A response header that lists which sources a page may load scripts and styles from. A per-request nonce is how inline styles are allowed without opening every inline style.; See also: Middleware

See also: Static asset

Used in: Full-Stack Web App
Static asset: A file served as it is: CSS, JS, images, fonts. It has no handler and no session, which is why it can be cached far longer than a page.; See also: Cache header

See also: Cache busting

Used in: Full-Stack Web App
Template: A file of markup with blanks filled in at render time. A template holds the shape of one page; the data it is given is what makes it a different page.; See also: Route

See also: Partial

Used in: Full-Stack Web App
Partial: A small template included by others, like the page head or footer. One partial means one place to change, and every page changes with it.; See also: Template

Used in: Full-Stack Web App
Render: Drawing a frame: clearing the canvas and painting every object in order. The order is the depth, so a later draw is a thing in front.; See also: Game loop

See also: Frame

Used in: Endless Platformer

AI and models

The vocabulary of a model that answers text, and the things built on it.

LLM: A large language model: a model that predicts the next piece of text after a prompt. It is a text predictor, not a database, which is why it can invent a plausible wrong fact.; See also: Token

See also: Prompt

See also: Hallucination

Used in: LLMs

Used in: Local LLMs
Token: A small piece of text, often part of a word, which is the unit a model reads and charges for. "4000 tokens" is not 4000 words, and the split is why long words cost more.; See also: LLM

See also: Context window

Used in: LLMs
Prompt: The text a model is given before it answers. A prompt states the task, the shape of the answer, and what not to do; the model follows the shape more reliably than it follows the prose.; See also: System prompt

See also: Context window

Used in: Prompting

Used in: LLMs
System prompt: The standing instructions a model is given before any user text, holding role, tone, and format. It is the right place for rules that must hold for every answer.; See also: Prompt

See also: Temperature

Used in: Prompting
Context window: The most text a model can consider at once, counted in tokens. Anything longer has to be cut, summarised, or retrieved, which is why a long document is not simply pasted in.; See also: Token

See also: Retrieval augmented generation

Used in: LLMs
Embedding: A list of numbers that represents a piece of text, arranged so similar meanings sit close together. Similarity becomes arithmetic, which is how search over meaning works.; See also: Vector

See also: Retrieval augmented generation

Used in: LLMs
Vector: An ordered list of numbers. An embedding is a vector, and comparing two vectors is how "closest match" is computed.; See also: Embedding

See also: Array

Used in: LLMs

Used in: Quant
Retrieval augmented generation: Fetching the passages that actually match a question and putting them in the prompt, so the model answers from real sources instead of memory. It is the fix for a model that invents.; See also: Embedding

See also: Hallucination

Used in: AI Agents

Used in: LLMs
Hallucination: A model producing confident text that is not true. It is the default behaviour of a text predictor, and the reason a model's answer must be checked against a source.; See also: Retrieval augmented generation

See also: Evaluation

Used in: LLMs
Temperature: A setting that widens or narrows the model's choice of next token. Zero picks the most likely continuation every time, which is what a deterministic task needs.; See also: Prompt

See also: LLM

Used in: Prompting
Fine-tuning: Continuing training on examples of one task, so the model learns that shape. It changes behaviour, not knowledge, which is why it is the wrong tool for "teach it this fact".; See also: Prompt

See also: Retrieval augmented generation

Used in: LLMs
Agent: A model that runs a loop: decide, call a tool, read the result, decide again. The plan is the model's, the actions are real, and the loop needs a step limit.; See also: Tool calling

See also: Retrieval augmented generation

Used in: AI Agents
Tool calling: A model choosing a named function and arguments from a list it was given, instead of writing the answer itself. The code runs the call, which is where the model stops being the thing that computes.; See also: Agent

See also: Function

Used in: AI Agents
Streaming: Sending a model's answer as it is produced, token by token, instead of waiting for the whole reply. A reader starts reading sooner, and a bad answer can be stopped mid-way.; See also: Token

See also: LLM

Used in: AI Chatbot

Used in: LLMs
Evaluation: Running a model against a fixed set of questions with a fixed expected answer, and scoring the result. An eval is how a change to a prompt is proven to be an improvement.; See also: Hallucination

See also: Regression

Used in: LLMs
Quantization: Storing a model's numbers in fewer bits, trading a little accuracy for a much smaller and faster file. It is why a model that needs 13GB can run on a laptop in 4GB.; See also: LLM

See also: Local model

Used in: Local LLMs
Local model: A model that runs on the machine instead of behind an API. Nothing is sent away and there is no per-call cost, which is the trade: privacy and offline use for a smaller, weaker model.; See also: Quantization

See also: LLM

Used in: LLMs

Version control and workflow

The words for changing code with others, and shipping it safely.

Repository: One folder plus its recorded history: the files, the changes, and who made each one. A repository is the record, not the folder, which is why deleting the folder deletes the record.; See also: Commit

See also: Branch

Used in: Git & Version Control

Used in: GitHub Essentials
Commit: One saved set of changes with a message and a fingerprint. A commit is the unit of "this state works", and it is the thing a bisect walks through.; See also: Repository

See also: Diff

Used in: Git & Version Control
Branch: A separate line of commits you can work in without touching the main one. A branch is cheap and disposable, which is why a small fix belongs on one.; See also: Repository

See also: Merge conflict

Used in: Git & Version Control

Used in: GitHub Essentials
Diff: The difference between two versions, shown as added and removed lines. Reading a diff is how a change is reviewed, because it names exactly what changed.; See also: Commit

See also: Code review

Used in: Git & Version Control
Merge conflict: Two branches that changed the same lines, where the tool cannot choose. The markers show both sides and your job is to pick one, not to delete the block.; See also: Branch

See also: Rebase

Used in: Git & Version Control
Rebase: Moving your commits to sit after someone else's, so the history reads as one line. It rewrites your commits, which is why a branch already shared with others is not rebased.; See also: Merge conflict

See also: Branch

Used in: Git & Version Control
Pull request: A proposed set of changes opened for review before it is merged. It is the review, the discussion, and the CI run in one place.; See also: Code review

See also: CI/CD

Used in: GitHub Essentials

Used in: Git & Version Control
Code review: Reading a proposed change before it is merged, looking for what breaks rather than what is styled wrong. A review that finds only style is reviewing the wrong thing.; See also: Pull request

See also: Regression

Used in: GitHub Essentials
CI/CD: Automated checks on every change: build, test, then deploy. It is the machine that catches the regression you forgot, before a person does.; See also: Pull request

See also: Test runner

Used in: CI/CD Pipelines

Used in: GitHub Essentials
Test runner: The program that runs a suite and reports pass or fail per case. A suite that passes but tests nothing is the failure mode, which is why every assertion names what it checked.; See also: CI/CD

See also: Regression

Used in: CI/CD Pipelines
Semantic versioning: A version number of major, minor, and patch, where the first digit means a breaking change. It is how a reader knows which release a note describes.; See also: Package manager

See also: Release

Used in: Git & Version Control
Release: A tagged commit marked as shipped, with notes about what changed. A tag is a permanent name for one commit, which is how a regression is bisected against a known good state.; See also: Semantic versioning

See also: Commit

Used in: Git & Version Control
Container: A packaged set of programs and files that runs the same way on any machine. It is how "works on my machine" becomes "works here", with the toolchain inside it.; See also: Environment variable

See also: Deploy

Used in: Go

Used in: Full-Stack Web App
Deploy: Putting a built version somewhere it is served from, and knowing which version is live. A deploy that cannot be rolled back is not a deploy, it is a bet.; See also: Release

See also: Cache busting

Used in: CI/CD Pipelines

Game building

The words for the loop a game runs in, from the endless-platformer track.

Game loop: The repeating three steps of a running game: read input, update the world, draw the frame. Everything about a game is placed into those three steps.; See also: Render

See also: Delta time

Used in: Endless Platformer
Frame: One drawn picture in the sequence. Sixty frames a second is the target; a frame that takes longer than 16 milliseconds is the reason a game stutters.; See also: Game loop

See also: Delta time

Used in: Endless Platformer
Delta time: The real time since the last frame, used to scale movement. Speed is written as units per second, so the game runs the same on a slow machine and a fast one.; See also: Frame

See also: Game loop

Used in: Endless Platformer
Hitbox: The simple shape used for touching, usually a rectangle smaller than the drawn art. Players feel fair when the hitbox is a little forgiving rather than exact.; See also: Collision detection

Used in: Endless Platformer
Collision detection: Deciding whether two shapes overlap. Rectangles are compared with four inequalities, which is why almost every 2D game starts with boxes rather than outlines.; See also: Hitbox

See also: State machine

Used in: Endless Platformer
State machine: A set of named states and the allowed moves between them: running, jumping, falling, dead. Naming the states is what makes an impossible transition impossible.; See also: Collision detection

See also: Game loop

Used in: Endless Platformer
Procedural generation: Building content from a rule and a seed instead of storing it. The same seed gives the same level, which is how a random level can still be tested.; See also: Seed

See also: Game loop

Used in: Endless Platformer
Seed: The starting number a random generator is given. Fixing it makes a random run reproducible, which is the difference between a testable bug and an unrepeatable one.; See also: Procedural generation

See also: Random number generator

Used in: Endless Platformer
Random number generator: A source of numbers that look unpatterned. A seeded generator is reproducible, which is what a game needs; a true random source is not, which is what a lottery needs.; See also: Seed

See also: Procedural generation

Used in: Endless Platformer

Used in: Quant
Canvas: The browser element you draw pixels into with code. It holds no elements and no styles, which is why a canvas game has no DOM to inspect.; See also: Render

See also: DOM

Used in: Endless Platformer

Used in: JavaScript
Input handling: Turning key and mouse events into game intent, and holding that intent in a set of currently-held keys rather than reacting to single presses.; See also: Game loop

See also: State machine

Used in: Endless Platformer

Terminal, shell and data

The words for working through a terminal and reading data as text.

Working Directory: The place a shell answers from. Relative paths are read against it, so the same command means different things in different directories.; See also: Path

Used in: Terminal & Shell
Path(file path): The name of a file or folder. An absolute path starts at the root of the drive; a relative path starts at the working directory.; Used in: Terminal & Shell
Pipe(|): Sending the output of one command into the input of the next. Each stage transforms text, and the chain is the program.; See also: Working Directory

Used in: Terminal & Shell

Used in: Build a CLI Tool
Redirection: Sending a command to a file instead of the terminal, with > for output and < for input. The same two streams a pipe joins.; See also: Pipe

See also: Redirect

Used in: Terminal & Shell

Used in: Build a CLI Tool
grep: Finding the lines that match a written pattern. The pattern is a rule about text, not a name of a file.; See also: Regular Expression

Used in: Terminal & Shell

Used in: Data Analysis
Regular Expression(regex): A small pattern language for text: character classes, repetition, and alternation. It describes the set of strings a matcher accepts.; See also: grep

Used in: Terminal & Shell

Used in: Testing & Debugging
Glob: A path pattern with * and ? that names many files at once. The shell expands it before a command sees any arguments.; See also: Path

Used in: Terminal & Shell

Used in: Build a CLI Tool
Standard Input(stdin): The one stream a command reads text from: typed, piped, or redirected. A tool that reads stdin works on any source.; See also: Pipe

Used in: Terminal & Shell

Used in: Build a CLI Tool
Standard Output(stdout): The one stream a command writes its answer on. Results go here so a pipe can read them; notes and errors go elsewhere.; See also: Standard Input

Used in: Terminal & Shell

Used in: Build a CLI Tool
Exit Code: The number a command returns to say whether it succeeded: zero means yes, anything else means no. A script branches on it.; See also: Standard Output

Used in: Terminal & Shell

Used in: Build a CLI Tool
CSV: Rows of values separated by one character, with the first row naming the columns. The simplest table that a text file can hold.; See also: Table

Used in: Data Analysis
Pivot: Re-arranging a table so a category runs across the columns instead of down the rows, which is the shape a chart or a summary wants.; See also: CSV

Used in: Data Analysis
Percentile: The value at a given position in a sorted list, so half the values sit below the median. It describes a distribution without averaging it.; See also: CSV

Used in: Data Analysis
SQL: The language a database reads: name the rows you want, the columns you want, and how they are joined. The database decides the steps.; See also: Query

See also: Table

Used in: SQL & Databases
Table: Named columns holding one value per row: one thing per row, one property per column. Adding a column is a design decision, not a new file.; See also: CSV

Used in: SQL & Databases
Assertion(assert): A written claim that a value must hold, checked by running the code. A failing assertion names the promise that broke.; See also: Test runner

Used in: Testing & Debugging
Breakpoint: A line marked so the program stops there on its own, leaving the values on the screen to be read instead of guessed.; See also: Debugging

Used in: Testing & Debugging
Mock: A stand-in object that answers a call with a written value, so a test measures one piece without the real thing behind it.; See also: Assertion

Used in: Testing & Debugging

Web surface and access

The words for what a browser asks for, sends back, and lets a reader reach.

HTTP Header: A name and value sent with a request or a response, carrying the meaning around the body: what type the body is, what may be cached, what may be embedded.; See also: HTTP status code

See also: Cache header

Used in: HTTP & APIs

Used in: Web Performance
curl: A command that makes one HTTP request and prints the response, so an API can be read from a terminal before any client code exists.; See also: Standard Output

Used in: HTTP & APIs
Rate Limit: A written ceiling on how often a caller may ask, answered with a status when the ceiling is passed. The limit is part of the contract.; See also: HTTP Header

Used in: HTTP & APIs

Used in: Go Web Servers

Used in: Python Flask Apps
HSTS: A header that tells a browser to use https for a site from now on, so an http address is corrected before a request is made.; See also: Content Security Policy

Used in: Security
Dependency Audit: Checking the packages a project pulls in against a list of known problems, so a fix is a version change in the lock file.; See also: Lock File

Used in: Security
Alt Text: The words a screen reader speaks in place of an image. Text that only repeats the file name describes the file, not the picture.; See also: DOM

Used in: Web Accessibility

Used in: HTML & CSS
Focus Ring: The outline drawn on the control a keyboard is on right now. Removing it without a replacement hides where the reader is.; See also: Input handling

Used in: Web Accessibility

Used in: HTML & CSS
Landmark: A named region of a page: navigation, main content, footer. A reader can jump to a region instead of walking through every element.; See also: DOM

Used in: Web Accessibility

Used in: HTML & CSS
Contrast Ratio: The measured gap between text colour and its background. A number below the line is unreadable to part of the audience, not unfashionable.; See also: Alt Text

Used in: Web Accessibility
DevTools: The browser panel that measures a page: requests, timings, layout, and listeners. The measurement lives there, not in a guess.; See also: HTTP Header

Used in: Web Performance

Used in: Frontend Testing
Compression: Sending a body in a smaller form and saying so in a header, so the transfer costs less and the reader unpacks it the same way.; See also: Static asset

Used in: Web Performance
Performance Budget: A written limit on what a page may spend: bytes, requests, milliseconds. A number nobody can name is not a budget.; See also: DevTools

Used in: Web Performance
Flexbox: A one-axis layout: items share a line and the rules say how they grow, shrink, and space out when the line changes width.; See also: Landmark

Used in: HTML & CSS
Grid: A two-axis layout: rows and columns are declared once and items are placed into them, so the shape is written rather than implied.; See also: Flexbox

Used in: HTML & CSS
Design Token: A named value for a colour, space, or font size, written once and used everywhere, so a change is one edit instead of a hunt.; See also: Variable

Used in: HTML & CSS

Used in: Web Performance
Headless Browser: A real browser run from a script with no window open, so a page can be driven and measured in a test rather than by hand.; See also: Test runner

Used in: Frontend Testing

Systems, runtimes and numbers

The words for programs that run close to a machine, serve a socket, or hold money.

Callback(continuation, handler function): A function handed to other code so that code can call it once the work it was asked for is done. The other code decides when and how often it runs, which is why a callback body has to be safe to run more than once.; See also: Runtime

Used in: Async & Concurrency
Concurrency(concurrent work): Several streams of work open at the same time, so each one can be waiting while another runs. The streams do not have to run in the same order every time, which is what makes the order a thing to design instead of a thing to assume.; See also: Race condition

Used in: Async & Concurrency
Thread(thread of execution): A separate stream of instructions inside one process, scheduled by the runtime so several of them make progress at once. A thread has no return channel, so a value it produces has to be left in a place someone else reads.; See also: Concurrency

See also: Runtime

Used in: Async & Concurrency
Task(async task, scheduled job): One piece of work the runtime can hold open, move around, and finish on its own schedule. A task is a value, so it can be started now and waited for later, which is what lets several waits overlap.; See also: await

See also: Concurrency

Used in: Async & Concurrency
Lock(mutex, mutual exclusion): A gate around a section of code that lets only one writer inside at a time. A lock does not stop a writer that takes a different lock, so every writer of one value has to name the same gate.; See also: Race condition

Used in: Async & Concurrency
Deadlock(standstill): Two holders each waiting for what the other holds, so neither can move and nothing raises an error. The shape needs a cycle, so one stated order for taking every lock removes the cycle for all of them.; See also: Lock

Used in: Async & Concurrency
Timeout(time limit, wait cap): A limit on how long a wait may stay open before it reports. The limit stops the waiting, not the work, so a task that timed out still has to be cancelled to free the resource it holds.; See also: Task

Used in: Async & Concurrency
Sentinel(stop signal, end marker): A value put into a stream that means the stream is over rather than being work. A worker that reads one stops, which is the only way an empty queue is told apart from a finished one.; See also: Queue

Used in: Async & Concurrency
Idempotent(safe to repeat): An action that leaves the same result when it runs twice as when it runs once. A callback that may be called more than once, or a request that may be retried, only behaves well when the action is idempotent.; See also: Callback

Used in: Async & Concurrency
await: A marker on a call that finishes later, telling the runtime to pause this function and come back with the value when it arrives.; See also: Runtime

Used in: Rust Async & WASM
Executor: The piece that decides which ready task runs next on a thread. An async function only works because something schedules it.; See also: await

Used in: Rust Async & WASM
WebAssembly(WASM): A binary instruction format a browser can run, close to machine speed, with the host deciding what it may touch.; See also: Runtime

Used in: Rust Async & WASM
Host Limits: The ceiling a caller sets on what a guest program may use: memory, time, and which functions it may call.; See also: WebAssembly

Used in: Rust Async & WASM
Route Table: The written set of method plus path pairs a server answers, kept in one place so the contract can be read and diffed.; See also: Route

Used in: Go Web Servers

Used in: Python Flask Apps
Connection Pool: Reusing the same few sockets instead of opening one per request, so the cost of setting up a connection is paid once.; See also: Race condition

Used in: Go Web Servers
Graceful Shutdown: Stopping a server by finishing the requests it already accepted before closing, so no reader gets a half answer.; See also: Transaction

Used in: Go Web Servers
App Factory: Building the application object inside a function instead of at import time, so configuration and state are set before anything runs.; See also: Route Table

Used in: Python Flask Apps
Fixed Step: Advancing a simulation in equal slices of time regardless of frame rate, so the same input gives the same result on any machine.; See also: Delta time

Used in: Game Dev beyond Canvas
Swept Collision: Testing the whole path a fast object travelled in one step instead of only where it landed, so it cannot pass through a wall.; See also: Collision detection

Used in: Game Dev beyond Canvas
Difficulty Curve: The written plan for how much pressure a game adds over time, so a change is a number in a table rather than a new level.; See also: Fixed Step

Used in: Game Dev beyond Canvas
Greeks: The names for how an option contract moves: delta for time, gamma for the curve, theta for the whole picture. They are vocabulary, not formulas.; See also: Vector

Used in: Quant Extensions
Kelly Sizing: Sizing a stake from the edge and the odds, so a run of good bets cannot be undone by one oversized loss.; See also: Greeks

Used in: Quant Extensions
Walk Forward: Testing a rule on data it has not seen yet, one window at a time, so a result cannot come from fitting the past.; See also: Percentile

Used in: Quant Extensions
Portfolio Risk: The total a whole set of positions can lose at once, which is what a size limit is written against, not each trade alone.; See also: Kelly Sizing

Used in: Quant Extensions

Building a tool from scratch

The words for a program that reads input, transforms it, and reports what it did.

Lexer: The first pass that turns characters into named pieces: number, name, symbol. Everything downstream reasons about pieces, not letters.; See also: Token

Used in: Build a Compiler
Grammar: The written rules for which arrangements of pieces are legal programs, usually one rule per kind of expression.; See also: Lexer

Used in: Build a Compiler
Parse Tree: The nested shape a grammar builds from a flat list of pieces, so order of operations comes from the shape and not from a rule.; See also: Grammar

See also: Tree

Used in: Build a Compiler
Pass: One full walk over the tree that makes one kind of decision, repeated as a list of steps so each step can be read alone.; See also: Parse Tree

Used in: Build a Compiler
Bytecode: The flat stack instructions a program becomes after the tree, small enough to store and simple enough to run anywhere.; See also: Pass

See also: Runtime

Used in: Build a Compiler
Inverted Index: A map from each word to the documents that contain it, built once so a lookup costs the same whatever the size of the text.; See also: Hash map

Used in: Build a Search Engine
Postings List: The sorted list of document numbers stored under one word, so two words can be intersected by walking two lists.; See also: Inverted Index

Used in: Build a Search Engine
Ranking: Scoring each hit by how well it matches and how often the words appear, then ordering by the score rather than by arrival.; See also: Postings List

Used in: Build a Search Engine
Front Matter: The block of name and value pairs at the top of a content file, read before the prose so metadata and body never mix.; See also: JSON

Used in: Build a Static Site Generator
Template Hole: A marked gap in a template that one named value fills, with the value escaped so content cannot become markup.; See also: Template

See also: Render

Used in: Build a Static Site Generator
Link Graph: Every link a page makes, held as pairs of source and target, so a broken address is an edge with no destination.; See also: Graph

Used in: Build a Static Site Generator
Manifest: The written file that names what a tool may reach and how it is loaded, read as the contract before any code runs.; See also: JSON

Used in: Build a Chrome Extension
User Style: A rule a tool adds to a page after it is loaded, so a change is a written instruction rather than a rewrite of the page.; See also: Template Hole

Used in: Build a Chrome Extension
Lock File: The written file that records exactly which versions of which packages a project pulls in, so the same install gives the same tree on another machine.; See also: Package manager

See also: Dependency Audit

Used in: Versioning & Releases

Used in: Docker & Containers
Keyed Storage: A tool keeping its own values under names, so state survives a page reload without touching the page again.; See also: Session

Used in: Build a Chrome Extension
Arguments(argv): The words a command receives after its name, read as a written shape: which are flags, which are values, which are names.; See also: Exit Code

Used in: Build a CLI Tool
Dry Run: Printing the changes a command would make without making them, so a plan can be read and checked before it is applied.; See also: Arguments

Used in: Build a CLI Tool

Used in: Build a Static Site Generator
Build Report: The summary a tool writes about what it did: counts, warnings, and failures, used to decide whether a run counts as done.; See also: Dry Run

Used in: Build a Static Site Generator

Used in: Build a Chrome Extension

Used in: Build a CLI Tool

AI tools, in practice

The words for what an AI tool reads, changes, and reports back - and for checking it.

AI Coder: An editor that writes code beside you: it reads the file you are in and offers the next few lines. The file is its only context unless you give it more.; See also: Agent

See also: Inline Suggestion

Used in: AI Coder
Inline Suggestion: The next few lines an editor offers at the cursor, which you take or reject. Accepting one without reading it is how a subtle change gets in.; See also: AI Coder

Used in: AI Coder
Context Window Fill: The files an assistant is actually shown when it answers. Naming them is the difference between a guess and an answer about your code.; See also: Context window

Used in: AI Coder
Chunking: Splitting documents into pieces small enough to be compared one at a time, with the overlap between pieces decided before the split.; See also: Embedding

See also: Token

Used in: Retrieval & Embeddings
Vector Search: Finding the stored pieces nearest a question, measured in directions rather than words, so a different phrasing still reaches the same fact.; See also: Embedding

See also: Inverted Index

Used in: Retrieval & Embeddings
Citation: The source a claim is traced back to. An answer without one is a sentence nobody can check.; See also: Hallucination

Used in: Retrieval & Embeddings
Training Set: The written examples a model is later tuned on: input paired with the answer it should give. A few dozen good pairs beat a few hundred vague ones.; See also: Fine-tuning

Used in: Fine-tuning
LoRA: Teaching a model a small addition instead of rewriting it, stored as its own file that can be loaded, swapped, or dropped.; See also: Training Set

Used in: Fine-tuning
Loss Curve: The score of how wrong a training run is, plotted over the steps. A curve that stops moving says the run taught nothing.; See also: Training Set

Used in: Fine-tuning
Golden Set: The questions with the answers they must give, written down once and kept, so a model is scored against the same list every time.; See also: Evaluation

See also: Assertion

Used in: LLM Evals
Rubric: The written rules a judge model scores an answer against, so a score is a claim about named criteria rather than a feeling.; See also: Golden Set

Used in: LLM Evals
Pass Rate: The share of a golden set a model answers well enough. It is the number a release decision is written against.; See also: Golden Set

Used in: LLM Evals
Eval Gate: Refusing a change when the score falls below a written line, so a model update cannot ship on a worse number than the one before it.; See also: Pass Rate

See also: Build Report

Used in: LLM Evals
Fence: The written marks that separate instructions from the text being worked on, so pasted content is read as data and not as a command.; See also: System prompt

Used in: Prompt Injection & AI Security
Escape: Text that closes a fence early and starts a new instruction, which is what a written rule about data has to survive.; See also: Fence

Used in: Prompt Injection & AI Security
Canary String: A value written into a prompt that no reader would ever type. If it appears in the answer, something outside the prompt was read.; See also: Escape

Used in: Prompt Injection & AI Security
Tool Scope: The named set of actions a model may ask for, with the rest refused. A model that can ask for anything cannot be limited by words alone.; See also: Tool calling

Used in: Prompt Injection & AI Security