Like all ruminants, they are members of the order Artiodactyla, the even-toed ungulates. Although the name "sheep" applies to many species in the genus Ovis, in everyday usage it almost always refers to Ovis aries.
Numbering a little over one billion, domestic sheep are also the most numerous species of sheep. They are most likely descended from the wild mouflon of Europe and Asia. One of the earliest animals to be domesticated for agricultural purposes, they are raised for fleece, meat (lamb, hogget or mutton) and milk. Their wool is the most widely used animal fibre, and is usually harvested by shearing. Ovine meat is called lamb when from younger animals and mutton when from older ones.