Explosive jumping
From Halopedia, the Halo wiki
Grenade Jumping, or occasionally known as Grenade Hopping, is a trick where the player throws a Grenade onto the ground and jumps as it goes off, using the force of the grenade to propel them forward. It is usually done with the Plasma Grenade, as the sticking nature is easier to work with. You can get to higher places with this trick. Also, it's very fun. If the player has got the Sputnik skull, grenade jumping will be twice as effective but note that skulls only take effect in campaign and grenade jumping will be normal in any type of multiplayer game.
This can also be done by aiming down with a Rocket Launcher, then shoot and jump at the same time or, if you have an Overshield, both a grenade and a rocket.
(to do this on Xbox Live you need to be host)
