Flap steak, or flap meat is a beef steak cut. It comes from a bottom sirloin butt cut of beef, and is generally a very thin steak. It is sometimes confused with hanger steak as they both are thin and come from similar parts of the animal. Like skirt or flank steak, flap meat benefits from marinating and being cooked on high, dry heat, whether grilled, broiled, pan-fried or stir-fried. It's vital to cut the meat very thinly across the grain and it is at its best not too much past medium-rare. U.S. raised grass-fed beef.