Wikipedia
Strafe-jumping
Strafe-jumping is a form of trickjump used to increase a player's speed in computer games based on the Quake engine. The technique is common in Quake II, Quake III Arena, Quake 4, QuakeLive, OpenArena, CodeRED: Alien Arena, Nexuiz, Xonotic, Cube, Jedi Knight II, Star Wars Jedi Knight: Jedi Academy, Soldier of Fortune II, Doom 3, Warsow, Digital Paintball 2, Call Of Duty, Return to Castle Wolfenstein, Wolfenstein: Enemy Territory, Tremulous, Unvanquished and Counter-Strike.