chuck roast is what part of the cow
The typical chuck steak is a rectangular cut, about 1" thick and containing parts of the shoulder bones, and is often known as a "7-bone steak," as the shape of the shoulder bone in cross section resembles the numeral' 7'. This cut is usually grilled or broiled; a thicker version is sold as a "7-bone roast" or "chuck roast" and is usually cooked with liquid as a pot roast.