The term grammar actually has more than one meaning. It refers both to the language user's subconcious system, and to the linguist's attempts to describe that system. It also refers to the abstract system loosely constructing all languages, as well as the system which makes up a particular language.

It can also refer to a certain school of linguistic thought, or to a specific collection of facts for an audience. However, all these uses seek to explain the same phenomena: morphology and syntax.

Morphology is the study of the smallest units of grammar that have meaning, or how words are formed. Syntax means the structural organization of language at the sentence level, or more succinctly, how words are combined.