A standing rib roast, also known as prime rib, is a cut of beef from the primal rib, one of the nine primal cuts of beef. While the entire rib section comprises ribs six through 12, a standing rib roast may contain anywhere from two to seven ribs. It is most often roasted “standing” on the rib bones so that the meat does not touch the pan. The prime rib is well-marbled throughout its meat, meaning that it has a decent amount of fat content that renders down as it cooks to keep the beef tender. A popular way to cook the rib is with au jus, or in its own juices, to prevent it from getting dry during the cooking process as it reaches your desired temperature.