Grammar is the set of structural rules governing the composition of clauses, phrases, and words in any given natural language.
A specific description, study or analysis of such rules may also be referred to as a grammar. A fully explicit grammar that exhaustively describes the grammatical constructions of a language is called a descriptive grammar. It may be used more broadly, including rules of spelling and punctuation, but rather as a part of orthography.
The formal study of grammar is an important part of education for children from a young age through advanced learning, though the rules taught in schools are not a "grammar" in the sense most linguists use the term, particularly as they are often prescriptive rather than descriptive. Prescriptive grammar is taught in primary and secondary school. The primary focus has been to prevent the use of outdated prescriptive rules in favor of more accurate descriptive ones and to change perceptions about relative "correctness" of standard forms in comparison to non-standard dialects.