Flap steak

Flap steak, or flap meat (IMPS/NAMP 1185A, UNECE 2203) is a low-end beef steak cut. It comes from a bottom sirloin butt cut of beef, and is generally a very thin steak. Flap steak is sometimes called sirloin tips in New England, but is typically ground for hamburger or sausage meat, elsewhere. 
The flap steak is sometimes confused with the higher quality hanger steak. The item consists of the obliquus internus abdominis muscle from the bottom sirloin butt. The cut is sometimes inaccurately sold as skirt steak.