Swing down mount
There’s a lot going on here with the naming of this element, surprising because it’s actually named after no one. The swing down itself is known as a Korbut, so you’ll hear this skill most often called a Korbut mount…because you’re doing a Korbut as a mount.
There’s also a variation on this skill—seen in the GIF above—with tucking and stretching of hips in the air before the swing down, a mount that was named after Lavinia Milosevici for a time before the WTC decided that it didn’t constitute a different mount compared to the regular swing down. That skill on the beam, with the tucking and stretching in a swing down, was originally known as a Chen flic, so you might also see that particular mount referred to as a Chen mount, since it’s a Chen used as a mount.
Simple simple simple.