In linguistics, grammar is the set of logical and structural rules that govern the composition of sentences, phrases, and words in any given natural language. The term refers also to the study of such rules, and this field includes morphology and syntax, often complemented by phonetics, phonology, semantics, and pragmatics.
Each language has its own distinct grammar. "English grammar" is the set of rules within the English language itself. "An English grammar" is a specific study or analysis of these rules. A reference book describing the grammar of a language is called a "reference grammar" or simply "a grammar". A fully explicit grammar exhaustively describing the grammatical constructions of a language is called a descriptive grammar, as opposed to linguistic prescription, which tries to enforce the governing rules of how a language is to be used.
Grammatical frameworks are approaches to constructing grammars. The standard framework of generative grammar is the transformational grammar model developed in various ways by Noam Chomsky and his associates from the 1950s onwards.