1. The domesticated variety of the European polecat (Mustela putorius furo), a mammal of the weasel family (Mustelidae) that is about 50 cm long with a brown, black, and white coat. They are carnivores, most active around dawn and dusk, and live contentedly in groups. Traditionally they were kept for hunting (ferreting), mainly for rodents, moles, and rabbits. Today they are kept mainly as pets.

2. (black-footed ferret) A North American mustelid, Mustela nigripes, that is nocturnal and feeds mainly on prairie dogs. At one time it was hunted for its fur. Its numbers have declined, due mainly to the reduction in prairie dog populations as prairie grasslands were brought into cultivation, and the ferret is now endangered, though its numbers have increased through a captive-breeding programme.