Originating from the dirty-dirty (South of the US), referring to rims that literally stick out from the tyres, this slang also refers to - put simply - a woman's backside. However, and herein lies the crux of the slang; not every woman's ass (or arse) can be described as such. Some women (rather unfortunately) have a flat ass, regardless of whether it is large in circumference or not. Much to my joy, some women with a small butt have what can be described as a poke-out. As long as it protrudes, preferably with the arch in the back (kai, i love that!), please describe it as a poke-out. Anything else is an imitation.
Damn, sonny, look at dat hispanic mami wit da poke-out. (Grits his teeth, under his breath: son, I love dat bitch.) I wanna work dat from da back!