An animal that hunts other animals for food is called a carnivore or predator. These animals must kill other smaller animals to feed. Since carnivores must hunt to survive, they use large amounts of energy to obtain their food, and thus they require many calories to stay healthy.
Predators serve a valuable role in an ecosystem by keeping the population of herbivores in check. If there are not enough predators to kill plant-eating animals, then the animals overpopulate the area. Then, the herbivores would not be able to find enough food. An overabundance of herbivores also threatens to eradicate plant life and vegetation in the area.