Formal language

A set of finite strings over an alphabet, specified by a rule or computational device. Formal languages provide precise ways to describe syntax and patterns.

Alphabet (formal languages): A finite or otherwise specified set of symbols from which strings are formed. Every string in a formal language is built from symbols in its alphabet.
Regular expression: A notation that describes regular languages using union, concatenation, and repetition. Regular expressions provide concise descriptions of languages built from simple pattern operations.
Compiler: A program that translates source code from one programming language into another representation. Compilers use formal language descriptions to recognize and process programming-language syntax.
Formal semantics: The mathematical assignment of meaning to expressions in a formal system or programming language. Formal language describes which strings are valid; semantics specifies what those strings mean.
String (computer science): A finite sequence of symbols drawn from an alphabet. A formal language consists of strings, including possibly the empty string.
Finite-state machine: A computational model with finitely many states and transitions between them. A finite-state machine recognizes a language by accepting or rejecting each input string.
Parsing: The process of analyzing a string according to a grammar's structural rules. Parsing determines whether an input has grammatical structure and what that structure is.
Natural language: A language that develops and changes through use among human communities. Unlike formal languages, natural languages are not generally fixed by a complete explicit rule system.
Empty string: The unique string containing no symbols, commonly denoted ε. Whether ε belongs to a language affects its grammar and automaton descriptions.
Pushdown automaton: A finite-state machine equipped with a stack, giving it memory for nested structures. Its stack lets it recognize languages beyond finite-state machines, such as balanced parentheses.

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