Vacio, suadero, arracheras - YouTube.

Matambre, also known as suadero in some Latin American countries, is the name of a very thin cut of beef in Argentina, Paraguay and Uruguay, taken from between the skin and the ribs, a sort of flank steak. It is not the cut known normally in the U.S. as flank steak. It is a rose colored muscle taken between the skin and the ribs.