Rabbit hopping, or "strafe jumping," is a popular technique used by players of Left 4 Dead 2 to move faster and avoid enemy attacks. To perform a rabbit hop, simply hold down the strafe key while moving forward. This will cause your character to move faster and make it more difficult for enemies to hit you.
There are a few things to keep in mind when strafe jumping. First, you will need to have enough space to perform the maneuver. Second, you will need to be moving in a straight line; if you try to strafe jump while moving around objects or corners, you will likely end up running into something. Finally, remember that strafe jumping will not make you completely invincible; enemies can still hit you if they are close enough.
With those tips in mind, go out and start strafe jumping your way to victory!