Teres major is a cut of beef that comes from the chuck section of the cow.
The petite tender is also known as the shoulder tender, the teres major, or the bistro filet. It is a relatively thin strip of muscle from the shoulder, and is unusually fine-grained, with a lot of the same characteristics as tenderloin. In fact, many people consider the petite tender to be nearly as good of a cut as the tenderloin, and at a lower price-point.
You can use the petite tender as a direct substitute for tenderloin in most recipes.
It also happens to be one most tender cuts from a cow!