The rib eye or ribeye (known as Scotch fillet in Australia and New Zealand) is a boneless rib steak from the rib section.

Ribeye steaks are mostly composed of the longissimus dorsi muscle but also contain the complexus and spinalis muscles. The longissimus dorsi is also referred to as the "eye of the ribeye". The spinalis is also referred to as the "ribeye cap" and the complexus is a small muscle at the front of the ribeye which may be trimmed off by the butcher.

It is both flavoursome and tender, coming from the lightly worked upper rib cage area which spans from the sixth to twelfth ribs of the cattle. Its marbling of fat makes it very good for fast and hot cooking.

More Info: en.wikipedia.org