Butterflying
From Halopedia, the Halo wiki
Butterflying is a glitch that occurs in Halo 2 and Halo 3. The glitch allows two players to, through cooperation, fly through the air. In Halo 3, one person has to jump on the other's head repeatedly, while the other person keeps on pressing RB and B repeatedly in a sparse repetition; the button combination "cancels" a reload and a beat down to a lock on sequence, allowing you to fly. In Halo 2, you press B and X repeatedly with any weapon (Energy Sword is recommended), to achieve the same result.