The eye of round steak comes from the "round" primal cut, specifically the center of the round, which is a lean, heavily used muscle in the cow's hindquarters. It's a very lean cut of beef, meaning it has a lower fat content compared to other cuts like ribeye or tenderloin. Due to its leanness and the muscle's heavy use, eye of round steak can be tougher than other cuts, so slow cooking methods like braising or roasting are recommended to tenderize it. Despite its leanness, eye of round steak has a good beef flavor, and it's a good option for dishes where the flavor of the beef is the main focus. Marinating can help to tenderize the steak and enhance its flavor.