A large plastic bottle with two holes burnt into it, one at the base and one at the "dome" of the bottle. A spliff is then inserted into the hole at the base, and someone sucks through the top of the bottle while holding the other hole, which is usualy refered to as the "hit" hole. You toke through the bottle whilst holding the hit hole until the bottle fills up with smoke or "creams". Then, you take your finger off the hit hole and suck in as much smoke as you can. This shit fucks you up, try it some time.
Dude, lemme get a hit of your zoomie.