Lamb, hogget, and mutton are the meat of domestic sheep. The meat of an animal in its first year is lamb; that of an older sheep is hogget and later mutton.

Because of dramatically differing economic values of each type of animal (lamb being the most expensive), classification systems have developed to ensure consumers receive the product they have purchased. The strict definitions for lamb, hogget and mutton vary considerably between countries. General definitions include:

• Lamb — a young sheep that is less than one year old.
• Baby lamb — a milk-fed (not yet weaned) lamb between six and eight weeks old.
• Spring lamb — a milk-fed lamb, usually three to five months old, born in late winter or early spring and sold usually before July 1st.
• Yearling lamb — a young sheep between 12 and 24 months old.

Read More in Wikipedia "Lamb and Mutton" »  

See also "Lamb" in the Epicurious Food Dictionary.