A sheep is in the class mammalia, so it is a mammal. The domestic sheep is the most populous of the sheep species, and there is a good reason. Sheep are often used as a way to get wool for yarn and fabric. The meat is also considered to be a well-loved dish - with mutton from an older sheep and lamb meat is from a younger sheep, usually called a lamb.
The sheep also make milk, so sheep’s milk is often harvested from sheep who are not slaughtered for their meat. Sheep have been used as sacrificial animals in a variety of religions - Christianity, Aramaic religions, and more. They are often used as symbols for the pure and innocent in the world.