In grammar, a conjunction (abbreviated CONJ or CNJ) is a part of speech that connects words, phrases, or clauses, which are called its conjuncts. That description is vague enough to overlap with those of other parts of speech because what constitutes a "conjunction" must be defined for each language. In English, a given word may have several senses and in some contexts be a preposition but a conjunction in others, depending on the syntax. For example, after is a preposition in "he left after the fight" but a conjunction in "he left after they fought".
In general, a conjunction is an invariant (non-inflecting) grammatical particle that stands between conjuncts. A conjunction may be placed at the beginning of a sentence, but some superstition about the practice persists. The definition may be extended to idiomatic phrases that behave as a unit and perform the same function, e.g. "as well as", "provided that".
