In games, like Quake, rocket jumping is a technique where a player fires a rocket at the ground, wall, or other surface and, at the same time, they jump to travel at a greater distance. In the game, this is a skill play which can propel the player into a higher, more advantageous position. For instance, it may allow him or her to escape another player or establish an exclusive vantage point for sniping. Because you take damage and is part of the game, it is not considered cheating.
There is a similar tactic called grenade jumping, where the player places a grenade at their feet or below a vehicle to propel themselves or an object into the air.