A predator (lion, tiger, cheetah...) is the animal that goes hunting for the prey (gazelle, deer, zebra...). When the prey is killed, the scavenger (hyena, vulture...) comes in to the scene and tries to steel the meal from the predator. In conclusion , the scavenger prefers to steal a freshly killed meal, than go hunting for his own. If he failed to steel the meal, he waits for the predator to eat, and comes in and eat the remains after the predator has left.
A predator feeds on other LIVING things, while the scavenger eats animals that are already dead.