is used to describe several things:
As an adjective, definitive describes something which is considered an authoritative, final or conclusive example or version of its type.
In philately, a definitive is a common issue postage stamp that is part of a complete series, covering all available denominations.
In published works, and especially in literature, a definitive version of a work or a part of that work or an interpretation thereof is the one that is accepted as the "correct" one.
latin root of definitive: serving to provide a final solution or to end a situation.