Lamb neck is a particular part of lamb, but the specific area varies based on the country of the butcher. Commonly the term is used in Britain to describe an area of the animal that is part of the back and behind what non-butchers would call the neck. This cut of meat contains spinal bone and connective tissue, but a butcher can remove the bone for customers. Typically tough and strongly flavored, lamb neck is suitable for braising or slow-cooking.
British butchers call the part of the animal that is between the back and the head "scrag end" of lamb. The portion of the animal that they define as "lamb neck" is further along the back on top of the shoulders. In fact, three different parts of the lamb can be termed "neck." These are middle neck, best end of neck, and confusingly, scrag end can also go by the name "neck end."
Middle neck is a portion of the animal behind the scrag end that reaches about a third of the way down the back of the animal. Both the scrag end and the middle neck contain lots of bones from the spine and a high proportion of connective tissue and fat. Although they can be cooked with the bone in, it is possible to take the bone out and roll the remaining meat into a joint for oven roasting. The fat and connective tissue means that the cut is best with slow cooking, and a cook may dice the meat up or grind it to speed up the cooking process.
Behind the middle neck is the best end of neck. This is a portion of the lamb that runs from the first rib to the eighth rib of the animal. Less tough than the middle neck or neck end, a butcher can portion this into lamb cutlets or keep it whole as a roast. The cut of lamb immediately behind the best end of neck is the loin. Typically, due to the leanness of the meat in the best end, this cut is more expensive than the other two cuts that are part of the lamb neck.
In the U.S., for example, this British terminology is not used. The U.K. terminology refer to the area of the lamb below the scrag end and middle neck as shoulder, whereas the American format is to use "shoulder" to refer to the part of the lamb from where the front legs come out of the body up to the back and including the neck. Shoulder roast and lamb shoulder neck slices are examples of the specialized cuts from this area. Terminology can differ from country to country, but primarily, when a butcher refers to lamb neck, he or she means a part of the animal that includes spinal bones from the first half of the animal.