What tenderloin means
Tenderloin is the American name for the long, narrow, cylindrical muscle that runs along the inside of the backbone, beneath the loin, in beef, pork and lamb. In Britain, it is usually called fillet, as in beef fillet and pork fillet. Because this muscle does very little work, it is the most tender cut of meat, with a fine, soft, buttery texture, though its flavour is milder than that of harder-working cuts. Each animal has only a small amount of tenderloin, which makes it expensive, especially in beef.
Beef tenderloin, or fillet, is cut into steaks such as fillet steak, known as filet mignon in the US, tournedos and chateaubriand, a thick centre cut for sharing. It is roasted whole, wrapped in pastry for beef Wellington, sliced raw for carpaccio and steak tartare, and cut into strips for stir-fries and stroganoff. Pork tenderloin is a small, lean, inexpensive cut, ideal for roasting whole, cutting into medallions or strips, stuffing and wrapping in bacon. Because tenderloin is lean, it cooks quickly and can easily become dry if overcooked, so it is best seared and roasted briefly, often to medium-rare for beef, and rested before slicing.
The tough silverskin is trimmed off before cooking. It differs from the loin, the larger cut above it. You will see tenderloin in American recipes and fillet in British ones.