In linguistics, grammar is the set of rules for how a natural language is structured, as demonstrated by its speakers or writers. Grammar rules may concern the use of clauses, phrases, and words. The term may also refer to the study of such rules, a subject that includes phonology, morphology, and syntax, together with phonetics, semantics, and pragmatics. There are, broadly speaking, two different ways to study grammar: traditional grammar and theoretical grammar. Fluency in a particular language variety involves a speaker internalizing these rules, many or most of which are acquired by observing other speakers, as opposed to intentional study or instruction. Much of this internalization occurs during early childhood; learning a language later in life usually involves more direct instruction. The term grammar can also describe the linguistic behaviour of groups of speakers and writers rather than individuals. Differences in scale are important to this meaning: for example, English grammar could describe those rules followed by every one of the language's speakers. At smaller scales, it may refer to rules shared by smaller groups of speakers. A description, study, or analysis of such rules may also be known as a grammar, or as a grammar book. A reference work describing the grammar of a language is called a reference grammar or simply a grammar. A fully revealed grammar, which describes the grammatical constructions of a particular speech type in great detail is called descriptive grammar. This kind of linguistic description contrasts with linguistic prescription, a plan to marginalize some constructions while codifying others, either absolutely or in the framework of a standard language. The word grammar often has divergent meanings when used in contexts outside linguistics. It may be used more broadly to include orthographic conventions of written language, such as spelling and punctuation, which are not typically considered part of grammar by linguists; that is, the conventions used for writing a language. It may also be used more narrowly to refer to a set of prescriptive norms only, excluding the aspects of a language's grammar which do not change or are clearly acceptable (or not) without the need for discussions. Source: Wikipedia (en)