What term is used to describe an animal that eats both plants and other animals to derive energy?

The term that describes an animal that eats both plants and other animals to derive energy is a consumer. Consumers are organisms that rely on other living beings for their nutritional needs. This group includes various entities such as herbivores, carnivores, and omnivores.

In the context of the options provided, herbivores are animals that eat only plants, while decomposers break down dead organic matter to recycle nutrients back into the ecosystem. Producers, on the other hand, are organisms like plants that produce their own food through photosynthesis. Therefore, the only term that encompasses animals consuming both plants and animals is 'consumer'.