Omnivores (from Latin: omni, meaning "all, everything"; vorare, "to devour") are species that eat both plants and animal material as their primary food source. They often are opportunistic, general feeders not specifically adapted to eating and digesting either meat or plant material primarily. Many depend on a suitable mix of animal and plant food for long-term good health and reproduction.

Omnivore, omnivory and similar derivations are terms of convenience; their significance varies according to context and the requirements of communication in a range of fields in which such attributes are matters of both kind and degree. No rigid non-fuzzy definition therefore is either possible or necessary. Traditionally the definition for omnivory is some variation of the form: "including both animal and vegetable tissue in the diet", which is clear enough for most purposes. However, it is neither absolute nor yet precise, either exclusively or inclusively. It is in fact barely meaningful, because most herbivores and omnivores eat only a small range of types of plant food; there is little value to classifying an omnivorous pig digging for roots and small animals, with an omnivorous chameleon that eats leaves as well as insects; the two have little ecological or dietary overlap.

The term "omnivory" also is not comprehensive because it does not deal with questions of mineral food such as salt licks, or the question of eating life forms that are not included in the kingdoms Animalia and Plantae. As for appeals to etymological points such as that "omnivore" means "eater of everything", no biologist or philologist would take them seriously.