The sirloin steak is a steak cut from the upper middle of the cow (British and Australian butchery)
In British and Australian butchery, the word sirloin refers to cuts of meat from the upper middle of the animal, similar to the American short loin.
In U.S. butchery, the steak is cut from the rear back portion of the animal, continuing off the short loin from which T-bone, porterhouse, and club steaks are cut. The sirloin is actually divided into several types of steak. The top sirloin is the most prized of these and is specifically marked for sale under that name. The bottom sirloin, which is less tender and much larger, is typically marked for sale simply as "sirloin steak". The bottom sirloin in turn connects to the sirloin tip roast.
How Sirloin got its name
In 1617, James I stayed for 3 days at Hoghton Tower in Lancashire. So enamoured by the hospitality shown to him by Sir Richard Hoghton he felt compelled to reward his host in a fitting manner. Before he was about to consume an exquisite loin of beef, he unsheathed his sword and knighted the side of beef with the words: "Arise Sir Loin".
It may or may not be true, but it's a nice story!