lamb is a young sheep or meat derived from a young sheep. Mutton is meat from adult sheep. Goat meat is called chevon, or cabrita. However, in USA, if you go to an arabic food store, they call it goat meat. Also what you call the cooked goat meat depends on the cut of meat you are cooking. here is a good website to explain the cuts: http://www.americanlamb.com/lamb-cutting-board/#shoulder-chop Hope this helps.

Lamb is a Juvenile sheep, whereas mutton is the meat of an adult or mature sheep.