This section of the hind leg of beef extends from the rump to the ankle. Since the leg has been toughened by exercise, the round is less tender than some cuts. There are six major sections into which the round can be divided: the rump; the four main muscles (top round, sirloin tip, bottom round and eye of round); and the heel. The rump is a flavorful triangular cut taken from the upper part of the round. It's generally cut into rump steaks or two or three roasts that when boned and rolled are referred to as rump roasts. Those with the bone in are called standing rump roasts. Pieces from the rump section are best cooked by moist-heat methods. The top round, which lies on the inside of the leg, is the most tender of the four muscles in the round. Thick top-round cuts are often called butterball steak or London broil, whereas thin cuts are referred to simply as top round steak. The boneless sirloin tip is also called top sirloin, triangle and loin tip. The better grades can be oven-roasted; otherwise moist-heat methods should be used. The bottom round can vary greatly in tenderness from one end of the cut to the other. It's usually cut into steaks (which are often cubed) or the bottom round roast. The well-flavored eye of the round is the least tender muscle, although many mistakenly think otherwise because it looks like the tenderloin. Both steaks and roasts from this cut require slow moist-heat cooking. A cut that includes all four of these muscles is usually called round steak and those cut from the top (and which are of the best grades) can be cooked with dry heat. Near the bottom of the round is the toughest cut, the heel of the round. It's generally used for ground meat but can sometimes be found as a roast.
From The Food Lover's Companion, Fourth edition by Sharon Tyler Herbst and Ron Herbst. Copyright © 2007, 2001, 1995, 1990 by Barron's Educational Series, Inc.