This steak is USDA Prime, the highest level of marbling recognized by the USDA.
Beef sold in the U.S. is graded by the United States Department of Agriculture (USDA). There are eight total grades and the top grade is USDA Prime.
Only about 4 to 5% of all beef graded in the U.S. has marbling to grade at this level. You can sometimes find USDA Prime at local butchers and higher-end grocery stores, but most of it goes to high end steakhouses and restaurants. Prime beef has excellent flavor and tenderness.
Marbling, or intramuscular fat, is the most important factor used to grade beef in the U.S. and around the world. This is determined by a visual inspection of the amount and distribution of intramuscular fat between the 12th and 13th rib. Historically, this single inspection provides a correct indicator of the entire carcass.