1. Referring to that which is clearly and unquestionably accurate: Hank wrote a very definitive article about the shooting incident at the elementary school which made it possible for others to see how the students and teachers were reacting to such a horrible situation.
2. Relating to something that can't be argued about or changed, final, and settled: The judge made a very definitive ruling which none of the lawyers could challenge.

Something is definitive when it is authoritative and serves as a final solution to a problem.