Tri-tip is a small cut of beef from the bottom sirloin with a fairly lean, quintessentially “beefy” flavor. It ranges from 1 1/2 to 3 pounds (680 g to 1.4 kg) and is magnificently easy and inexpensive to make for a large party. Its triangular shape yields slices of beef in varying degrees of doneness—some are rare, others are well done, and most are perfectly in between.