Skirt steak is a thin, long cut of beef from the diaphragm muscles of the cow. Skirt steak has an even more intense beefy flavor than flank steak. It does contain more tough muscles than flank steak, though, so should only be cooked to rare or medium-rare for the most tender texture. Flank steak comes from the flank of the steer below the loin and sirloin. It sits in the abdominal area of the animal near the bottom. It helps the cow to twist and walk, so the muscle works A LOT. It is tough, lean and has long thick muscle fibers.