All I know is it's a way to make a gun such as an AR shoot in auto mode by doing something with the trigger or something.  What is it, how do you do it, and how does it work?

I think you basically keep your trigger finger still and let the gun rebound off your shoulder or hip.  As it rebounds, the trigger hits your finger discharging another round.  Don't know for the details because I've never had a need for unaimed pseudo-automatic fire.

Bump firing is hard to decribe, it's something you actually got to see to understand. Go to www.redstararms.com they have a few clips on it. More or less you use the recoil of the gun to shoot. Gotta see the video it will make more sense. I'm dying to go out and tke my shot at it.

if you don't know what it is the best way to describe it is just try it.
Put the gun to your hip level stick your trigger finger straight out so it is almost touching the trigger then with your left hand pull the gun into your finger once this happens the gun will recoil but if you have forward pressure it will fall back on the trigger and then all hell breaks lose, really fun but expensive.