A shotty is a waterpipe where the stem is blocked with a piece of cig or weed, and it is essentially a carb for the waterpipe. As you draw the smoke into the chamber the air pressure builds up around the stopper until it 'pops' into the chamber - the release of the air pressure acts like a carb and forces air into the chamber and the smoke into your lungs - really really quickly.

There are guides for making a shotty here at cannabis.com and also at totse.com