Grammar

"Grammar"refers to the structure of a language. To be a reasonably competent speaker of a language you must understand its grammar. Every speaker of English, for example, understands the difference between "Eddie phoned Teddie" and "Teddie phoned Eddie," because it's a rule of English grammar that the subject (or actor) typically comes before the verb and the object (or target of the action) typically comes after the verb. You may not be able to state the rule explicitly, and you may not be able to define a "subject," an "object," or a "verb," but you understand these concepts and rules tacitly or else you can't understand the language.