A predator is an organism that eats another organism. The prey is the organism which the predator eats. Predator and prey evolve together.
In an ecosystem, predation is a biological interaction where a predator (an organism that is hunting) feeds on its prey (the organism that is attacked). Predators may or may not kill their prey prior to feeding on it, but the act of predation often results in the death of the prey and the eventual absorption of the prey's tissue through digestion. It could also constitute a chase, stalking, or attack of prey.