A ribeye steak is a cut of beef taken from the rib section of a cow, which is one of the nine primal cuts. The ribeye is a boneless cut taken from the rib section of beef cattle, while the rib steak is a bone-in ribeye. The ribeye is mostly composed of the longissimus dorsi muscle but also contains the complexus and spinalis muscles. The spinalis is also referred to as the "ribeye cap" and is the most flavorful part of the ribeye. The ribeye is prized for its tenderness, flavor, and high level of marbling. It is a very tender cut of meat, containing more marbling than other cuts, and is best cooked over high heat. The USDA recommends cooking ribeye steaks to an internal temperature of 145°F. The average 4 oz serving of ribeye has about 220 calories, 24 grams of protein, and only 6 grams of fat.

In summary, the ribeye is taken from the rib section of a cow and is a boneless cut of meat that is prized for its tenderness, flavor, and high level of marbling. The ribeye cap, which is the most flavorful part of the ribeye, is also known as the spinalis muscle.