Rocket jumping
From DoomWiki.org
Rocket jumping is the using of the rocket launcher's splash damage to propel a player high and far, much more than he could jumping with his own means. Players using this technique often take a large amount of damage unless they are invulnerable, so this tactic is not often used outside speedrun games, where this method can help to save big ammounts of time. One use for rocket jumping is reaching to the secret exit in E3M6: Mt. Erebus