Thin Skirt is the costal muscle portion of the diaphragm. All white tendinous tissue not covering lean red muscle is removed.
This piece to be used in a BBQ, especially eating medium-rare. The grill temperature needs to be high, and don't forget to have a good bottle of wine to pair this juicy and tender cut.
France: Bavette d’aloyau
Germany: Dicker Bauchlappen