A sheep in its first year is a lamb and its meat is also lamb. A sheep in its second year and its meat are hogget. Older sheep meat is mutton.
Lamb is often sorted into three kinds of meat: forequarter, loin, and hindquarter. The forequarter includes the neck, shoulder, front legs, and the ribs up to the shoulder blade. The hindquarter includes the rear legs and hip. The loin includes the ribs between the two.
A 100g cut of cooked lamb delivers about 25 grams of protein, plus good quantities of potassium and vitamin B-12. It's also a good source of iron, magnesium, selenium, and omega-3 fatty acids. While that's good news, lamb is also a source of saturated fat.