A herbivore is an animal that eats plants and does not hunt other animals for food: cows, deer, rabbits, pandas on bamboo, many caterpillars chewing leaves. Science class sets it beside carnivore (meat) and omnivore (both). It is a classroom and nature-documentary word; you would not use it at the dinner table for a person. Though actually, “only plants” is the tidy school version. Some animals we call herbivores will nibble bone, eggshell, or an insect now and then; the label is about their usual diet, not a law of nature. And a giant panda lives on bamboo, so we call it a herbivore, even though it sits in the bear family, which is full of meat-eaters — the word tracks what goes in the mouth, not the family tree.