"Grungus" is a word used to describe
filth. It is both an adjective and a
noun. Things that are dirty/filthy are "grungus" or "covered in grungus."
The word is more than this: it is the embodiment of disgust and repulsion, and is typically used hyperbolically.
"
Sis wtf did you cook in here, the
kitchen is covered in grungus."
or
(reacting to something
gross) "That shit's grungus, bro."