The common oat (Avena sativa) is a species of cereal grain grown for its seed, which is known by the same name (usually in the plural, unlike other grains). While oats are suitable for human consumption as oatmeal and rolled oats, one of the most common uses is as livestock feed. Oats make up a part of the daily diet of horses, about 20% of daily intake or smaller, and are regularly fed to cattle as well. Oats are also used in some brands of dog food and chicken feed. Oat seeds are commonly marketed as cat grass to cat enthusiasts, since cats readily harvest and eat tender young oat, wheat, and some other grass sprouts.

The wild ancestor of Avena sativa and the closely related minor crop, A. byzantina, is the hexaploid wild oat A. sterilis. Genetic evidence shows the ancestral forms of A. sterilis grew in the Fertile Crescent of the Near East. Domesticated oats appear relatively late, and far from the Near East, in Bronze Age Europe. Oats, like rye, are usually considered a secondary crop, i.e., derived from a weed of the primary cereal domesticates wheat and barley. As these cereals spread westwards into cooler, wetter areas, this may have favored the oat weed component, leading to its eventual domestication.