The 7-bone roast is a beef cut used for pot roast. It is cut from the shoulder area of the animal and is known as a cut of "chuck." It is called a 7-bone roast not because it contains 7 bones, but because of the shape of the prominent bone. It is sliced across the shoulder blade bone, and the bone looks rather like a fancy rendition of the number 7. (Check both images for clarification.)
Chuck roasts are considered to be the best, most flavorful cuts for pot roasts.