From the Chuck
The petite tender (aka: teres major) is a small, seldom used shoulder muscle.
Shhh, this is our little secret: Due to lack of use, the petite tender is arguably the second most tender cut after the tenderloin. An excellent cut of beef for a dinner of 2. Can be pan seared, roasted or grilled.Recipes & Tips
Teres Major...ly...WRONG! (The verdict is in)
Braising tips - Esquire.com