The meat from a mature sheep, which is an animal that is 2 years old or older. The meat from sheep up to 1 year old is referred to as lamb and from 1 year to 2 years is called yearling meat. Mutton can be used in place of lamb, but it has a stronger flavor than lamb and generally requires 5 to 10 minutes additional cooking time per pound. It is also becoming much more difficult to find and may require a special order. Lamb, yearling, and mutton have a whitish fat covering the meat, called the fell. Some of the fell can be removed to allow for better absorption of juices, marinades, and other seasonings before cooking.