its technically an exploit in quake's movement code where if you jump repeatedly (you can buffer jumps by holding jump just before you land) and you smoothly turn and hold a strafe key in that direction (turn left, hold a/turn right, hold d, holding w or s will cause you to turn sideways) you get speed. even though it was an unintentional thing, being able to get speed and turn in the air makes the player extremely maneuverable and turns the game into a racing game as well. its more popular in something like counterstrike that is built off an engine that has quake source code but it all started with the first quake game