i belive it is the curved indent cut into the locking lever of a lock back, so its more ergonomic when you press it with your thumb, very smart. like on a endura lightweight.
David Boye has been around for quite a while. He's come up with many ideas. The indent in a locking bar is just one of them. Mr. Bob Terzuola learned how to make knives from a book written by David Boye many years ago.