A rooster, also known as a cockerel, cock or chanticleer, is a male chicken (Gallus gallus) with the female being called a hen.

Immature male chickens of less than a year's age are called cockerels. The oldest term is "cock", from Old English coc. The term "rooster" originates from the United States, while in the United Kingdom and Ireland the older term "cockerel" is more widely used. In North America, Australia and New Zealand "rooster" (a relative neologism) is almost always used, occasionally cockerel. "Cock" is in general use as the name for a male of other species of bird, for example "Cock sparrow". "Roosting" is the action of perching aloft to sleep at night, and is done by both sexes. The rooster is polygamous, but cannot guard several nests of eggs at once. He guards the general area where his hens are nesting, and will attack other roosters that enter his territory. During the daytime, he often sits on a high perch, usually 4–5 feet off the ground to serve as a lookout for his flock. He will sound a distinctive alarm call if predators are nearby.