Grammar is the filed of linguistics that covers the conventions governing the use of any given natural language. It includes morphology and syntax, often complemented by phonetics,phonology,semantics, anf pragmatics. Each language has its own distinct grammar. "English grammar" is the set of rules if the english language itself. "An english grammar" is a specific study or analusysis 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 exhaustuvely describing the grammatical cinstuins if a language is called a descriptive grammar,as opposed to linguistic prescription, which tiles to enfirce the governing rules of how a language is to be used.