Backus–Naur form

Backus–Naur form is a notation for context-free grammars that defines syntax through production rules, commonly used to specify programming-language syntax.

Context-free grammar: A formal grammar whose production rules replace one nonterminal with a string of terminals and nonterminals. Backus–Naur form is a notation for expressing this kind of grammar.
Extended Backus–Naur form: A family of grammar notations that adds conveniences such as optionality and repetition to Backus–Naur-style rules. It makes common patterns more compact than the original notation.
ALGOL 60: A programming language whose 1963 report used Backus–Naur notation to describe its syntax. Its report helped establish the notation as a practical language-specification tool.
John Backus: An American computer scientist who led the development of FORTRAN and contributed to programming-language notation. Backus’s name is one half of the notation’s standard name.
Production rule: A grammar rule stating which strings may replace a particular nonterminal. Production rules are the statements from which a Backus–Naur grammar is built.
Grammar ambiguity: A property of a grammar in which some string has more than one distinct parse tree. A Backus–Naur grammar can define syntax without uniquely determining its structure.
ISO C grammar: The formal grammar in the C language standard that specifies the language's syntactic structure. It demonstrates Backus–Naur-style productions applied to a widely used programming language.
Peter Naur: A Danish computer scientist who edited the ALGOL 60 report and helped popularize its grammar notation. Naur’s editorial work gave the notation the other half of its name.
Nonterminal symbol: A symbol in a grammar that can be expanded using production rules. Nonterminals name syntactic categories such as expressions or statements.
Recursive definition: A definition that uses the concept being defined as part of its own specification. Recursive productions express arbitrarily nested structures such as parenthesized expressions.

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