Sirloin is from the lower portion of the ribs, continuing off the tenderloin from which eye fillet is cut. It is a prime cut with a fine grain and some marbling, and extremely tender. Ideal for pan frying.
New Zealand pork sirloin roasts are lean but less expensive than pork tenderloins. They are difficult to carve if they are bone-in, so have your butcher bone, roll, and tie it.