Flat iron steak is the American name for the cut known as "butlers' steak" in the UK and "oyster blade steak" in Australia and New Zealand. This cut of steak

Steak

A steak is a cut of meat . Most are cut perpendicular to the muscle fibers, improving the perceived tenderness of the meat. In North America, steaks are typically served grilled, pan-fried, or broiled. The more tender cuts from the loin and rib are cooked quickly, using dry heat, and served whole...

 is from the shoulder

Shoulder

The human shoulder is made up of three bones: the clavicle , the scapula , and the humerus as well as associated muscles, ligaments and tendons. The articulations between the bones of the shoulder make up the shoulder joints. The major joint of the shoulder is the glenohumeral joint, which...

 of a beef animal. The steak encompasses the infraspinatus muscles of beef, and one may see this displayed in some butcher shops and meat markets as a "top blade" roast. Steaks that are cross cut from this muscle are called top blade steaks

Blade steak

The top blade steak is one that comes from the chuck section of the steer or heifer. The steaks are cross-cut from the top blade subprimal, also known as Infraspinatus. It has a line of tough connective tissue down the middle, creating a tough steak best suited to braising...

 or patio steaks. As a whole cut of meat, it usually weighs around two to three pounds; it is located adjacent to the heart of the shoulder clod, under the seven or paddle bone (shoulder blade or scapula). The entire top blade usually yields four steaks between eight and 12 ounces each. Flat iron steaks usually have a significant amount of marbling

Marbled meat

Marbled meat is meat, especially red meat, which contains various amounts of intramuscular fat, giving it an appearance similar to a marble pattern.- Selective breeding :Marbling can be influenced by selective breeding...

. Anatomically, the muscle forms the dorsal part of the rotator cuff of the steer. This cut is anatomically distinct from the shoulder tender

Shoulder tender

A shoulder tender also called beef shoulder petite tender, beef shoulder tender petite roast, bistro filet, rat or teres major steak is a cut of beef of the teres major muscle from the blade of the shoulder...

, which lies directly below it and is the teres major.

Restaurants, particularly upscale, have recently begun serving flat iron steaks on their menus. Especially popular are flat irons from Wagyu beef, as a way for chefs to offer more affordable and profitable dishes featuring Wagyū

Wagyu

refers to several breeds of cattle genetically predisposed to intense marbling and to producing a high percentage of oleaginous unsaturated fat. The meat from wagyu cattle is known worldwide for its marbling characteristics, increased eating quality through a naturally enhanced flavor, tenderness...

 or Kobe beef

Kobe beef

refers to cuts of beef from the black Tajima-ushi breed of Wagyū cattle, raised according to strict tradition in Hyōgo Prefecture, Japan. The meat is generally considered to be a delicacy, renowned for its flavour, tenderness, and fatty, well-marbled texture. Kobe beef can be prepared as steak,...

. To make it more marketable, the steak, which has the fascia dividing the infraspinatus within it, has, in recent years, been cut as two flatter steaks, each corresponding to one muscle, with the tough fascia removed.

In the North American Meat Processor (NAMP) meat buyers guide, it is item #1114D Beef Shoulder, Top Blade Steak. The NAMP lists it as the second most tender cut, after the tenderloin, and followed (in order) by the top sirloin center cut, the ribeye and strip steak center cut, and finally beef shoulder, arm.