A bong is a device used to inhale smoke or vapour that uses a downpipe to filter the air through water before being inhaled.

Bongs have been used for centuries by indigenous cultures to inhale the smoke from herbal and natural remedies. By igniting plant matter at one end of a pipe that has the bottom hole in a small volume of water smoke can be drawn through a chamber to create a concentrated cloud before being inhaled. 

Read more about bongs here.