Programming Terms Explained
Short, exact definitions of the words you meet when you start to code. Each term has its own page with an example you can run in the browser, the mistakes people make with it, and links to the terms around it.
How code runs
What happens between the code you type and the program that runs: compilers, interpreters, runtimes and the operating system.
Source CodeSource code is the human-readable text of a program, written by a programmer in a language such as Python, Java or C and saved as plain text files, which a compiler or interpreter turns into instructions a computer can run.CompilerA compiler is a program that translates source code written in a programming language into machine code, or into another lower-level form such as bytecode, before the program runs. The translated program can then run without the original source.InterpreterAn interpreter is a program that executes source code directly, carrying out its instructions as it goes, instead of first translating the whole program into a separate machine-code file. The standard Python and Ruby implementations are interpreters.Runtime EnvironmentA runtime environment is the software a program needs around it while it runs: the engine that executes its code, the standard libraries it calls, and the services that manage memory, errors and access to the operating system. The JVM, Node.js and CPython are examples.Operating SystemAn operating system (OS) is the software that manages a computer's hardware and runs every other program, sharing the processor, memory and storage between them and giving them files, networking, input and output. Windows, macOS, Linux, Android and iOS are operating systems.
Building blocks
The pieces every program is made of: values, variables, arrays and loops.
VariableIn programming, a variable is a named place in memory that stores a value your program can read and change while it runs. The name, such as score or user_name, lets the code refer to the value without knowing where it is stored.BooleanIn programming, a boolean is a data type with exactly two values, true and false. Programs get booleans from comparisons such as age >= 18 and use them to decide which code runs, in if statements and loop conditions.ArrayAn array is a data structure that stores a collection of values of the same type in one continuous block of memory. Each value, called an element, is reached by its position number, called an index, which starts at 0 in most languages.IterationIn programming, iteration is repeating a set of instructions, usually with a loop, until a condition is met or every item in a collection has been processed. Each single pass through the repeated instructions is also called an iteration.
Errors and debugging
The three kinds of errors, how programs handle them, and the crash C programmers meet first.
Syntax ErrorA syntax error is a mistake in the structure of code, such as a missing colon, bracket or quotation mark, that breaks the grammar rules of a programming language. The compiler or interpreter rejects the program before any of it runs.Runtime ErrorA runtime error is an error that happens while a program is running, when an operation cannot be carried out with the values it has, such as dividing by zero or reading past the end of a list. The program stops at that line unless the error is handled.Logic ErrorA logic error is a mistake in a program's reasoning that makes it produce the wrong result without crashing or showing any error message. The code is valid and every line runs, but it does not do what the programmer intended.Exception HandlingException handling is a way for a program to respond to errors that occur while it runs. Code that might fail goes in a protected block, such as try, and when an error is raised, control jumps to a handler, such as except or catch, instead of crashing.Segmentation FaultA segmentation fault, or segfault, is a crash that happens when a program tries to read or write memory it is not allowed to access, such as address 0 through a null pointer. The operating system stops the program with the SIGSEGV signal.
Data and storage
How computers store data and check that it arrived intact: bits, bytes, checksums and databases.
BitA bit, short for binary digit, is the smallest unit of data in computing and holds one of two values, 0 or 1. Computers store and process all information, from numbers and text to images and programs, as sequences of bits.ByteA byte is a unit of digital data made of 8 bits, which together can represent 256 different values, from 0 to 255. On most computers it is the smallest unit of memory with its own address, and file sizes are counted in bytes.ChecksumA checksum is a short value calculated from a block of data, such as a file or a network packet, and stored or sent along with it. Calculating it again later and comparing the two values shows whether the data changed through corruption or a transmission error.DatabaseA database is an organized collection of data stored on a computer so that programs can find, add, change and delete it quickly and safely. It is managed by software called a database management system (DBMS), such as PostgreSQL, MySQL, SQLite or MongoDB.
Object-oriented programming
The ideas behind classes and objects: hiding data, sharing an interface and hiding detail.
EncapsulationIn object-oriented programming, encapsulation is keeping an object's data and the methods that work on that data together in one unit, usually a class, and hiding the internal details so other code can use the object only through its public methods.PolymorphismIn programming, polymorphism is the ability of one piece of code, such as a function call or a method name, to work with values of different types, each type supplying its own behavior. Calling shape.area() runs a different calculation for a circle than for a square.AbstractionIn programming, abstraction means hiding the details of how something works behind a simpler interface, so you can use it by knowing only what it does. Calling sorted(names) sorts a list without you writing, or even seeing, the sorting algorithm.
Frequently Asked Questions
What programming terms should a beginner learn first?
Do I need to know these terms before I start coding?
No. Most people learn them by writing small programs and looking a word up when it appears. A term sticks faster once you have seen the error or the output it describes.
Are programming terms the same in every language?
The ideas are. The names and details change: Python calls its array a
list and writes True, JavaScript writes true, and Java makes you declare a variable's type. Each page here notes where languages differ.Where can I practice these concepts?
Every term page has runnable examples you can edit in the browser. For structured practice, Coddy's free Python course walks through variables, loops, errors and classes one small exercise at a time.