Pork tenderloin comes from the loin a pig, inside the rib. Similar to beef tenderloin, it's the most tender cut of pork, and quite lean, too. Long, and narrow, whole tenderloin ranges from 3/4 lb. to 1-1/2 lb. Because it's relatviely inexpensive (there's virtually no waste on this boneless cut), widely available, and quick to cook, it's a great choice for weeknight cooking. (Though it can also be dressed up for a dinner party.) Its mild flavor partners well with many ingredients, and it's wonderfully versatile; you can cook it whole, slice it into medallions, butterfly and stuff it, or cut it into strips for stir-fry. It's delicious on the grill, roasted, and sautéed.
Boneless veal or chicken can work in some pork tenderloin recipes with some adaptation. Pork loin, which is not as tender, would take well to similar spice rubs and marinade used for pork tenderloin, but pork loin needs to be cooked longer and more slowly than tenderloin.
Look for all-natural tenderloins, which often have the best flavor and texture. Avoid pork that has been injected with additives, which can give the meat an unpleasant, rubbery texture. Try to use larger tenderloins (1 to 1-1/4 lb.), which tend to cook more gently and evenly than smaller ones; a larger tenderloin also yields fuller medallions for sautéing and often a more evenly shaped piece of meat for roasting whole.
Trim the pork of any silverskin, the thin membrane found on pork tenderloin and other cuts of meat. Trim excess fat or not; there's little of it, and this lean cut can benefit from it.
Keep refrigerated or freeze for longer storage.