What is Grammar?

Grammar definition and meaning on Dictionary terms:
the study of the way the sentences of a language are constructed; morphology and syntax.
these features or constructions themselves: English grammar.
an account of these features; a set of rules accounting for these constructions: a grammar of English.
Generative Grammar. a device, as a body of rules, whose output is all of the sentences that are permissible in a given language, while excluding all those that are not permissible.
prescriptive grammar.
knowledge or usage of the preferred or prescribed forms in speaking or writing: She said his grammar was terrible.

the elements of any science, art, or subject.
a book treating such elements.