The T-bone is a steak cut of beef. It consists of a T-shaped bone with meat on each side. The larger side contains meat from the strip loin, whereas the smaller side contains the tenderloin. Were these pieces of meat to be separated, you would have a strip steak and a small filet mignon. T-bone steaks from the rear end of the tenderloin contain a much larger section of the tenderloin, and are called porterhouse steaks.
Due to their large size and the fact that they contain meat from two of the most prized cuts of steak, t-bone steaks are generally considered one of the highest quality steaks, and prices at steakhouses are accordingly high. Porterhouse steaks are even more highly valued due to their large tenderloin.