Grenade Jump is a technique by which the player can launch a grenade while running in order to propel themselves up onto higher surfaces.
When the player is running with the MA-75 Assault Rifle/Grenade Launcher equipped, aiming the barrel at the floor and firing a grenade will cause the player to fly up higher than mere jumping would allow. If timed properly, this can allow the player to reach higher surfaces that would otherwise be unreachable.
Because a grenade is exploding at the player's feet, damage will be taken. Therefore it is best to use this technique while at full Shields.
The technique can also be used with the SPNKR SSM Launcher for even higher jumping, but with the downside of increased damage taken.