It is another word for fesis or poo. It is often used to describe the badness of something, either as prefix or suffix.
"I am going to see megadeth on tuesday."
"Do you not mean megabewg"
a cone piece packed with marijuana ready to be smoked through a bong
Simon: Nick how many bewgs did you have before the GAT?
Nick: only fourteen
Lachie: Bewgs mate!