A tender cut of beef taken from the rib primal. It is very tender, flavorful, and expensive. Prime rib is basically another name for a beef rib roast. Many people have the mistaken idea that the term "Prime Rib" refers to a roast that is graded "Prime" when actually the name has nothing to do with the grade or quality. Most of the roasts sold in supermarkets that are named "Prime Rib" are graded "Choice." Prime rib roasts that are graded "Prime" are usually available only to restaurants or through a special order with a butcher.