In grammar, conjunction (abbreviated conj or cnj) is a part of speech that connects words, phrases, or clauses that are called the conjuncts of the conjunctions. This definition may overlap with that of other parts of speech, so what constitutes a "conjunction" must be defined for each language. In general, a conjunction is an invariable (non-inflected) grammatical particle, and it may or may not stand between the items conjoined.
 

English Grammar Terms III

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.