A formal grammar describes how to form strings from an alphabet of a formal language that are valid according to the language's syntax. Wikipedia

A grammar describing a formal language Wikipedia Disambiguation

Strict observance of the established rules. OmegaWiki

A precise description of a formal language. OmegaWiki

A precise mathematical description of a formal language, consisting of terminal symbols, nonterminal symbols, a nonterminal symbol serving as start symbol, and a set of production rules that control the expansion of nonterminal symbols into strings consisting of both terminal and nonterminal symbols. Wiktionary

Description of a formal language. Wiktionary (translation)