Aggression--the snake comes toward you, seeking you out, to bite you.

Defense--the snake bites you if you come close enough to it, in order to drive you away.

I do not believe there are very many aggressive snakes in the world, and aggressive behavior is seen only in a few species--such as king cobras that defend their nesting areas.

I've never heard of an aggressive ball python that wasn't simply making a mistake (assuming that the warm thing is food instead of a person). All other bites are defensive, not truly aggressive. Ball pythons are not aggressive toward people. Fight/flight responses don't involve charging the target of their fear, the way they can in mammals. Balls don't deliberately seek out people to bite--it just doesn't happen.