Term referred to rap specifically referred to underground rap from australia, gutter typically is just a boom-bap type beat with someone with an australian accent rapping over it. A good example of this would be artists: Chillinit, Wombat, Nerve, Skrub, Triple One, Alex Jones, Mitchos Da Menace, Dunn Dee and many more
Chillinit: "Brudda brudda brudda
Did I stutterstutter?
This is gutter gutter for you motherfuckers"