Found this on the net....
What is a picanha? In American butcher-lingo it has been tragically baptized the “rump cap”. It is a triangular cut from the top of the, that’s right, rump region of the cow, and just like our rumps, it has a beautiful layer of fat. It is not a muscle that moves much during the animal’s life, and so, remains tender. The picanha’s blanket of fat lends the meat flavor and juiciness while protecting it from human error that may occur during grilling. And because it is little known in North America and Europe, a picanha is a relatively cheap and plentiful national secret. Oops. Did I just say something I shouldn’t have?