The pork tenderloin also in some countries called Pork Fillet, is a cut of pork. It is often sold as prepackaged products by large grocery stores. They are available plain (not seasoned) and flavored with a marinade.
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.
A pork tenderloin sandwich (also called simply a “tenderloin”) is a very thinly sliced piece of pork, usually the larger, tougher loineye (longissimus) muscle, uniquely battered and breaded, which is deep fried and served on a hamburger bun. This is usually served with mustard, ketchup, pickle and onions. This sandwich is generally sold in the US Midwest, especially in the US state of Indiana. In the southern states of the US, tenderloin is often prepared as a breakfast biscuit, usually with egg or cheese.