The ferret (Mustela furo) is a small, domesticated species belonging to the family Mustelidae. The ferret is most likely a domesticated form of the wild European ferret or polecat (Mustela putorius), evidenced by their interfertility. Other mustelids include the stoat, badger and mink.

Ferrets have a typical mustelid body-shape, being long and slender. Their average length is about 50 cm (20 in) including a 13 cm (5.1 in) tail. Their pelage has various colorations including brown, black, white or mixed. They weigh between 0.7 and 2.0 kg (1.5 and 4.4 lb) and are sexually dimorphic as the males are substantially larger than females. The average gestation period is 42 days and females may have two or three litters each year. The litter size is usually between three and seven kits which are weaned after three to six weeks and become independent at three months. They become sexually mature at approximately 6 months and the average life span is 7 to 10 years.

errets spend 14–18 hours a day asleep and are most active around the hours of dawn and dusk, meaning they are crepuscular. Ferrets have four types of teeth (the number includes maxillary (upper) and mandibular (lower) teeth) with a dental formula of 3.1.4.1 3.1.4.2 :