They are played differently?
Melee - The normal warcraft 3 game.
(Defense) TD - Build towers and defend against waves of monsters.
Hero Survival - This time you use heroes to defend against monsters.
(Offense) AOS - Two bases, heroes on each side, example: Dota.
ORPG - Online Role Playing Game. Usually with save/load these days.
RP - Role Play. I don't know how to explain that, ask someone else.
There's more but I can't be bothered to list them all.