Something soo ill and yet so clean. As seen with Immaculate, which means clean, spotless, it's used to describe something very "ill" thats perfect, spotless. Used in an exicted tense to compliment or intend to show the superiority of something. As someones pimping skills, which could be soo smooth, and perfect, or a song that is really tight.
Not sure the origin. It's out there, just not defined, and I randomly thought of it while sitting in a hot tub with some chicks and realized my pimping skills were "illmaculate".
Dang dude your pimping was soo illmaculate!
You rhymes are illmaculate!
That song is soooooo illmaculate dogg!