The subject in a simple English sentence, such as John runs, John is a teacher, or John was run over by a car, is the person or thing about whom the statement is made, in this case, John.

English Grammar Terms II

In linguistics, the grammar of a natural language is its set of structural constraints on speakers 'or writers' composition of clauses, phrases, and words. The term can also refer to the study of such constraints, a field that includes domains such as phonology, morphology, and syntax, often complemented by phonetics, semantics, and pragmatics. There are currently two different approaches to the study of grammar, traditional grammar and theoretical grammar.