It is another word for the region. It is also an acronym for northwest Indiana. It consists of Lake County and far west Laporte County. The acronym is used to make a not so cool place sound bad ass.
Dan: I don'y know what happened to Tommy Nuggets, he seems to be MIA.
Earl: MIA? That mothafucka ain't MIA. Mothafucka is NWI. He's mobbing deep, puffin on the dro, droppin bombs and shit.
Not worth it
I was going to be the kool-aid man, but i figured its nwi.