Short for "Mouth Bong". To use one's mouth as a water filtration system for smoking. This is done by holding water in your mouth, and then smoking while holding your head at a low angle, so as to let the water in your mouth filter the smoke, like a bong, and finally spitting the water out before exhaling.
Me and Bliz picked up some shwag, we gonna' back alley moutbong dis shit.
by gmnugget July 17, 2006