Think of chuck flat as boneless chuck ribs. Chuck flat is rich in flavor, this tender, versatile cut is often used for boneless short ribs, chuck streak, satays, fajitas, stir fry and sandwiches.
It is also used in Denver steaks and roasts. It is very similar to short ribs with delicate marbling and very popular at fancy restaurants as a "new discovered" cut similar to Delmonico.
In french it is called "Bifteck de bloc d'epaule" and "paleta de chocillo" in spanish.