Somersault Flip is a move used by Marshall Law and Forest Law, where they do a somersault flip kick. It is executed by pressing 3+4. By pressing 3 right after 3+4, the Laws will do another flip. It can also be executed by pressing u/f+4,3 and as of Tekken 6, it can only be performed that way.
There's many variations of this move, as it also serves as a combo ender for certain combo attacks, by pressing 3 or 4, depending on the combo attack the player perform. In addition to that, the characters Lee Chaolan, Paul Phoenix and Anna Williams have this kind of attack. It serves as one of Lee's combo enders. With Paul, stay crouched for a few seconds until Paul does an animation to get Ki Power, then press u+2+3+4 (u+3+4 from Tekken 6 onwards). With Anna, it is executed by pressing u+4 as of Tekken 6, but without the second somersault kick.