The pork tenderloin, also called pork fillet, is a long thin cut of pork.
As with all quadrupeds, the tenderloin refers to the psoas major muscle along the central spine portion, ventral to the lumbar vertebrae. This is the most tender part of the animal, because these muscles are used for posture, rather than locomotion.
In some countries, such as the US and The Netherlands ('varkenshaas'), pork tenderloin can be bought as a processed product, already flavored with a marinade. A common American dish is a pork tenderloin sandwich (also called simply a "tenderloin") – a very thinly sliced piece of pork, usually the larger, tougher loineye (longissimus) muscle, uniquely battered and breaded, which is deep fried and served in a hamburger bun, usually with garnishes such as mustard, ketchup, pickle and onions. This sandwich is generally sold in the US Midwest, especially in the state of Indiana. In the southern states, tenderloin is often prepared as a breakfast biscuit, usually with egg or cheese. It is quite common for pork tenderloin to be used as an alternative to beef tenderloin (usually called beef fillet in the UK), as it can be just as tender but costs significantly less.