In grammar, a conjunction is a part of speech that connects words, phrases, or clauses that are called the conjuncts of the conjoining construction. The term discourse marker is mostly used for conjunctions joining sentences. This definition may overlap with that of other parts of speech, so what constitutes a "conjunction" must be defined for each language. In English a given word may have several senses, being either a preposition or a conjunction depending on the syntax of the sentence (for example, "after" being a preposition in "he left after the fight" versus it being a conjunction in "he left after they fought"). In general, a conjunction is an invariable grammatical particle and it may or may not stand between the items conjoined.
This is a companion discussion topic for the original entry at http://grammarerror.com/tags/conjunction