What is rocket jumping?
Solution 1:
Rocket Jumping generally refers to a technique which is used to propel yourself using a rocket launcher. It generally requires that you are moving and then quickly aiming at the ground while you are still moving and firing your rocket launcher. Depending on the game you will take some damage, but will also move your character up in the air because of the force of the explosion of the rocket.
This video is a very good example of rocket jumping in Serious Sam.
Although personally I much prefer Freddie W's version.