The Long Jump (or Leap) is a special move featured exclusively in the 3D Mario games (excluding Super Mario Sunshine).
To perform the move, the player must crouch while in motion and then jump. It is most often used to go long distances that you otherwise could with a regular jump. It is also possible to move backwards while jumping, which can activate many glitches.
All characters playable in 3D platformers including Super Mario 64 DS can perform the long jump.