Short for gravity bong. A homemade or commercially available device used to consume cannabis by using water and air pressure to create a dense, powerful hit of smoke. Gravity bongs are typically made from simple materials like bottles or buckets, and they work by submerging a chamber in water, lighting the cannabis, and then lifting the chamber to fill it with smoke. When the chamber is pushed back down, the user inhales the smoke.
In the Wild — Example
We built a grav out of a two-liter bottle and a metal socket and it absolutely did not disappoint.
Have a better example? Suggest one.