Prey is an animal hunted for food. If you're a delicious-looking deer during hunting season, watch your back! You're the prey for all those guys in orange jackets carrying rifles.
Prey can also mean the human subject of an attack, or ridicule, by another person. Remember those bullies in school? The younger kids whom they shoved into lockers were their prey. Prey can also be used as a verb, meaning to hunt or go after. I bet most people would agree it's better to prey on something else than to be the preyed upon!