Gun Control & RKBA

A Semi-automatic means one shot per trigger pull.

An Automatic means the gun files more than one shot, typically continuous fire until empty (but in some guns, it can mean 2 or 3 shots, not continuous fire).

Bump firing a gun means that rather than pulling your finger towards the trigger, you are pulling the trigger towards your finger. The principal being that the recoil of the gun moves the gun back away from your finger so your continuous pulling of the gun towards your finger causes the gun to repeatedly bang into your finger. Its the same type of thing that happens when you first learn to drive a manual transmission and you let out the clutch too fast, jerking the car forward with you going back into the seat so when you lean forward, you hit the gas again, which then jerks you back into the seat and so on.

A bump fire stock is just a regular stock but one which can slide back and forth to make the process a bit easier. It takes a bit of practice to actually do because you can't push too hard or too soft.

HOWEVER, a bump fire stock is not necessary to bump fire. As some prior people mentioned, it can be achieved with a rubber band. In fact, the rubber band isn't needed at all, though it does make the process a bit easier.

Really, bump fire can be achieved using nothing but your finger, see the video below. How are you going to ban fingers?
(Jump to 1:44 in the video below for a demonstration.)