A particularly swampy sub-low bass sound used in Grime, Bass, UKG and other UK bred sub-genre's.
Similar to a filtered bass 'wob' sound. Often made in FM synthesizers or the VST Massive.
"Yo bruv', check this tune it's a properlygully riddim..."
"....Yeah g, that bass is proper making me want to fist a goat!"
Gully is when you need to get sick and crap at the same time, and when you throw up you gully yourself by crapping your pants or crapping on someone or something like the floor or a chair or a wall ect.
Wow, did you see him Gully. or He drank so much he gullied himself.