An omnivore is an animal that eats both plants and other animals. Humans are omnivores. Bears and pigs are omnivores too. A lion is not — a lion is a carnivore, which eats meat. A cow is not — a cow is a herbivore, which eats plants. Though actually, nature is less tidy than the school poster. Many animals we call carnivores eat a little plant matter, and some herbivores swallow insects by accident. Scientists still use omnivore because the main diet is mixed. People also use it about food choices: “I'm an omnivore” can mean “I eat meat and vegetables”, as opposed to a vegetarian. That is everyday talk, a little looser than biology, but well understood. The word is a noun. The adjective is omnivorous, which you may also see for a reader who will read almost anything.