Beef sirloin is a cut of beef taken from the hindquarter, between the short loin and the round, valued for a good balance of tenderness and rich, beefy flavor. It splits into top sirloin, tender enough for grilling and pan-searing, and bottom sirloin, tougher and better suited to braising or stewing.
In the UK, "sirloin" refers to a different section of the animal, roughly comparable to the American short loin/strip steak, so a British sirloin steak and an American sirloin steak are not the same cut.
Sirloin is commonly grilled, pan-seared, roasted, or braised, and pairs well with bold sauces such as chimichurri or a red wine reduction, plus starchy sides like roasted or mashed potatoes.