Beef is the meat of mature cattle. Most American cattle breeds are descendents of animals imported, possibly by the Vikings, during the early 1000s. Columbus and other early explorers also brought cattle on board their ships. Today, over 100 million head of cattle live in the United States and Canada. Beef is available in many different cuts, including steaks, roasts, brisket, stew meat, and ground beef. Tender cuts come from the ribs and loin. Tougher cuts come from the rump and shoulder. Prime beef has thin layers of fat, called marbling, running visibly through the muscle. Choice beef has little or no marbling but a layer of pinkish fat on the outer edges.