Flank steak is from the bottom abdominal area of the cow. This area of the cow gets quite a workout.  This cut of meat has a lot of tough fibers running through it and a very lean cut of beef.  A flank steak is thicker, and wider compared to a skirt steak.  In addition, generally the muscle fibers run lengthwise. Skirt steak is from the diaphragm muscles of the cow. The cut of meat is much thinner compared to a flank steak and is much longer. In addition, it is very lean cut of meat. We think it has even more tough muscle fibers than a flank steak.  The muscle fibers run horizontally across a skirt steak. Either a flank steak or skirt steak can be used in our Marinated Grilled Flank Steak recipe.