In zoology, an herbivore is an animal that eats only plants and no meat. Humans are not herbivores; rather, humans that choose not to eat meat are vegetarian. In practice, however, many herbivores will eat eggs and occasionally other animal protein.

Some herbivores can be classified as frugivores, which eat only fruit, and folivores, which specialize in eating leaves. This specialization is far from universal, however, and many fruit- and leaf-eating animals also eat other parts of plants, notably roots and seeds. The diets of some herbivorous animals vary with the seasons, especially in the temperate zones, where different plant foods are most available at different times of year.