Basically, my understanding is that it's a flip to the back in preparation for a flip that should land on the feet.
Our girls are doing bars DB timers to their backs on a mat -- release, flip one full rotation, and then around again to land "BOOM!" on the mat. It sounds painful but they all bounce up smiling afterward. This is the step after going into the pit.
The boys are also learning their rings DBs by going into the pit but aren't doing timers, except when it happens by mistake. DS, who is still somewhat floor challenged, now has a decent DB timer on tramp for progressing toward his floor DB. I expect it to be a long road!