Flank steak is a lean, flavorful cut from the cow's abdominal muscles, known for its long, flat shape and distinct grain, which can make it tough if not cooked properly. It benefits greatly from marinades and is best cooked quickly over high heat (like grilling or pan-searing) and sliced thinly against the grain to ensure tenderness, making it ideal for dishes like fajitas, stir-fries, and carne asada.