A beef tenderloin, known as an eye fillet in New Zealand and Australia, fillet in South Africa and the UK, filet in France and Germany, is cut from the loin of beef. As with all quadrupeds, the tenderloin refers to the psoas major muscle ventral to the transverse processes of the lumbar vertebrae, near the kidneys. The tenderloin is an oblong shape spanning two primal cuts: the short loin and the sirloin. The tenderloin sits beneath the ribs, next to the backbone. It has two ends: the butt and the "tail". The smaller, pointed end - the "tail" - starts a little past the ribs, growing in thickness until it ends in the "sirloin" primal cut, which is closer to the butt of the cow. This muscle does very little work, so it is the tenderest part of the beef. The tenderloin can be cut for either roasts or steaks. Tenderloins from steers and heifers are most common at retail, but those from cows are common in foodservice applications, such as less expensive steakhouses.
A common misconception is that the tenderloin is also called a Chateaubriand steak, when in fact, the Chateaubriand is a recipe for a particular tenderloin steak which originates from France. Typically, the Chateaubriand is taken from the center-cut of the tenderloin, in a large enough portion to feed two. There are three main "parts" of the tenderloin: the butt, the center-cut, and the tail. The butt end is usually suitable for carpaccio, as the eye can be quite large; cutting a whole tenderloin into steaks of equal weight will yield proportionally very thin steaks from the butt end. The center-cut is suitable for portion-controlled steaks as the diameter of the eye remains relatively consistent. The center-cut can yield the traditional filet mignon or tenderloin steak, as well as the Chateaubriand and Beef Wellington. The tail, which is generally unsuitable for steaks due to consistency of size concerns, can be used in recipes where small pieces of a tender cut are called for, such as Beef Stroganoff.
Whole tenderloins are sold as either "unpeeled" (meaning the fat and silver skin remain), "peeled" (meaning that the fat is removed, but silver skin remains), or as PSMOs ("pismos"), which is short for peeled, silver skin removed, and side muscle left on. While the most expensive option pound-for-pound, PSMOs offer considerable savings over other tenderloin options as they require little handling by the chef, since the fat and trimmings have already been removed. Trimming the silver skin from a tenderloin is a job best done by experts, as inexperienced meat cutters can damage the steaks, reducing either the yield or the visual presentation. Since it is the tenderest part of the animal, beef dishes requiring exceptionally tender meat, such as steak tartare, are ideally made from the tenderloin.