Kuuenbu

"With the correct timing, higher and further jumps are possible while airborne. Kuuenzan may be activated while attacking in the air."

- In-game text

Kuuenbu or Kūenbu (空円舞), is one of the two special techniques that Zero learns after defeating Split Mushroom in Mega Man X4. This technique allows Zero to jump a second time in midair -- by pressing the Jump button a second time -- allowing him to jump even higher to gain access to otherwise out-of-reach areas (provided that the player does not dash-jump beforehand).

Trivia

 * It is possible that this "move" indirectly appears in Tatsunoko vs. Capcom and Marvel vs. Capcom 3, with the obvious reason of why Zero can double jump in the game.
 * From this game onwards, along with the Hienkyaku, Zero can double jump and air dash for the rest of the X series onwards.