Programming Terminology — Grouped by Topic
Same terms as the main glossary, but organized by topic instead of alphabetically. Useful when you want to learn a whole area.
Variables & Data
Variable
A named container that stores a value you can read or change.
Constant
A variable whose value cannot be reassigned after it's set.
Identifier
The name you give to a variable, function, or class.
Literal
A value written directly in code, like 42, "hello", or true.
Data type
The category of a value — number, string, boolean, etc.
Integer
A whole number with no decimal part.
Float
A number with a decimal part (technically a floating-point number).
Boolean
A value that is either true or false.
String
Text — a sequence of characters wrapped in quotes.
Null
An explicit "no value" marker. Different from "undefined."
Undefined
In JavaScript: a variable declared but not assigned a value.
NaN
"Not a Number" — what some math operations produce when they can't return a real number.
Type coercion
Automatic conversion between types — common in JS, rare in Python.
Type casting
Explicitly converting a value from one type to another.
Immutable
A value that cannot be changed after it's created.
Mutable
A value that can be modified in place.
Control Flow
Conditional
Code that branches based on a true/false test.
If statement
The basic conditional construct.
Else
The branch taken when the if-condition is false.
Loop
Code that repeats until a condition is met.
For loop
A loop with an initializer, condition, and increment.
While loop
A loop that runs while a condition is true.
Iteration
One pass through the body of a loop.
Break
Exits the innermost loop immediately.
Continue
Skips to the next iteration of the loop.
Switch
A multi-way branch based on a single value.
Recursion
A function that calls itself.
Infinite loop
A loop whose condition never becomes false. Usually a bug.
Short-circuit evaluation
Logical operators stop early when the result is determined.
Truthy
A value that evaluates to true in a boolean context.
Falsy
A value that evaluates to false in a boolean context.
Functions
Function
A named, reusable block of code.
Method
A function that belongs to an object or class.
Parameter
A name listed in a function's definition for an input.
Argument
The actual value passed to a function when called.
Return value
The value a function gives back to the caller.
Side effect
A change a function makes outside its return value.
Pure function
A function with no side effects, returning the same output for the same input.
Callback
A function passed as an argument to be called later.
Higher-order function
A function that takes or returns another function.
Anonymous function
A function without a name, often used as a callback.
Arrow function
JavaScript's shorthand function syntax.
Closure
A function that "remembers" variables from its enclosing scope.
Recursion
A function that calls itself to solve a smaller version of a problem.
Scope
The region where a variable is visible.
Data Structures
Array
An ordered list of values, indexed by position.
List
Python's name for an array.
Object
A collection of named fields (key-value pairs).
Dictionary
Python's name for an object/map.
Map
A general data structure of key-value pairs.
Set
A collection with no duplicates.
Index
The position of an item in an array, starting at 0.
Key
The name used to look up a value in an object.
Value
The data associated with a key.
Tuple
An immutable, ordered group of values (mostly Python).
Stack
A last-in-first-out collection.
Queue
A first-in-first-out collection.
Tree
A hierarchical data structure with a root and branches.
Node
A single element in a tree or linked list.
Errors & Debugging
Bug
A defect — code that runs but produces the wrong result.
Error
An explicit failure thrown by the runtime.
Exception
An error that can be caught and handled.
Stack trace
The call path leading to an error, useful for debugging.
Syntax error
Code that doesn't parse (missing parenthesis, etc.).
Runtime error
An error that happens while the program runs, not when it's parsed.
Logic error
Code that runs without errors but produces wrong results.
Debugger
A tool that pauses code execution so you can inspect state.
Breakpoint
A place where the debugger pauses.
Console
The text-output area of a development environment.
Stack overflow
When recursion goes too deep and exhausts the call stack.
OOP
Class
A blueprint for creating objects.
Instance
A specific object created from a class.
Constructor
The function called when an instance is created.
Inheritance
One class extending another, gaining its members.
Encapsulation
Bundling data and behavior, hiding internal details.
Polymorphism
Using one interface for different types.
Abstraction
Hiding complexity behind a simple interface.
General
API
A set of routines or endpoints another program can call.
Compiler
A program that translates source code into another form (often machine code).
Interpreter
A program that runs source code line-by-line.
IDE
Integrated Development Environment — an editor with debugging, autocomplete, etc.
Library
Reusable code others wrote that you import.
Framework
A larger code base that imposes structure on your app.
Repository
A version-controlled folder of code, usually on git.
Commit
A saved snapshot of changes in version control.
Branch
A parallel line of development in version control.
Pull request
A proposal to merge one branch into another, with review.
Build
The process of turning source code into something runnable.
Deploy
Pushing code to a server where users can use it.
Refactor
Changing code's structure without changing what it does.
Technical debt
Shortcuts that make today easier but make future work harder.
Algorithm
A defined sequence of steps that solves a problem.
Pseudocode
English-like sketches of code, used for planning.
REPL
Read-Eval-Print Loop — an interactive prompt for running code.
Sandbox
An isolated environment to run untrusted or experimental code.