Beef flank

In the American system of primal beef cuts, the flank refers to the area right below the loin, and it stretches across the belly near the rear of the cow. It's a long, flat cut of beef that's very lean and contains a lot of tough fibers. Given its toughness and pronounced grain structure, flank steak is often marinated to tenderize it and then grilled or broiled quickly over high heat.

It's important to slice this cut across the grain to break up the muscle fibers and make it easier to chew. Flank steak is popular in a variety of dishes, including fajitas, stir-fries, and London broil. It's also the traditional cut used for corned beef.

Additionally, the flank is where "flap meat" comes from, which is a smaller cut within the flank that's often used similarly to flank steak. It's worth noting that even though flank steak is lean and tough, it's also known for its rich, deep, beefy flavor.