The sirloin is actually divided into several types of steak. The top sirloin is the most prized of these. The bottom sirloin is less tender, much larger, and is typically what is offered when one just buys sirloin steaks instead of steaks specifically marked top sirloin. The bottom sirloin in turn connects to the sirloin tip roast, which is generally considered to be a good, if somewhat tough, roast.
In fact, the word comes from the Middle English "surloine", which itself was derived from the Old French word "surlonge", meaning "sur la longe" or above the loin.. In Modern French, the term evolved to become "aloyau" or "faux-filet".