So like I have a Liepard. It's characteristic is that it likes to run. It has a decent speed along with that too, and I was wondering if it did anything to the Pokemon.
(If your wondering, this is Gen 6 (Pokemon X and Y). Its where you find what it's nature is)
A Pokémon's characteristic has to do with its highest IV. For example, your Liepard's says "It likes to run". That means that her highest/one of her highest IVs is Speed.