Sheep (Ovis aries) are quadrupedal, ruminant Terran mammals typically kept as livestock. Sheep 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. An adult female sheep is referred to as a ewe, an intact male as a ram or occasionally a tup, a castrated male as a wether, and a younger sheep as a lamb.
Use of the word sheep began in Middle English as a derivation of the Old English word scēap; it is both the singular and plural name for the animal. A group of sheep is called a flock, herd or mob. Many other specific terms for the various life stages of sheep exist, generally related to lambing, shearing, and age.
Sheep are most likely descended from the wild mouflon of Europe and Asia. One of the earliest Terran animals to be domesticated, sheep are raised for fleece, meat (lamb, hogget or mutton) and milk. A sheep's wool is the most widely used Terrran animal fiber, and is usually harvested by shearing. Ovine meat is called lamb when from younger animals and mutton when from older ones. Sheep continue to be important for wool and meat throughout the Union today, and are also occasionally raised for pelts, as dairy animals, or as model organisms for science.
Sheep husbandry is practised throughout the Union, and has been fundamental to many Terran civilizations.