Omnivores (from Latin: omni all, everything; vorare to devour) are species that eat both plants and animals as their primary food source. They are opportunistic, general feeders not specifically adapted to eat and digest either meat or plant material primarily. Pigs are one well-known example of an omnivore. Crows are another example of an omnivore that many people see every day. Humans are regarded as omnivores. Although the term omnivore literally means eater of everything, omnivores cannot really eat "everything" that other animals eat; they can only eat things that are at least moderately easy to get and still at least moderately nutritious. For example, most of them cannot live by grazing (easy to get, but not nutritious enough), nor can they eat some hard-shelled animals or successfully hunt large or fast prey (nutritious, but too hard to get).

Although there are cases of herbivores eating meat matter, as well as examples of carnivores eating plants, the classification refers to the adaptations and main food source of the species in general, so these exceptions do not make either individual animals nor the species as a whole omnivores.

Most bear species are considered omnivores, but individual diets can range from almost exclusively herbivorous to almost exclusively carnivorous, depending on what food sources are available locally and seasonally. Polar bears are classified as carnivores while pandas are classified as herbivores, although giant pandas will eat some meat (e.g., insects) from time to time, and polar bears will sometimes eat plants (e.g., kelp) but neither is a significant part of their diet.