UNDERGROUND HIPHOP

What exactly is underground hip hop. Is there any underground rappers that can score a hit on the pop charts? Yes In 1995 Funcky DEL the homosapien scored the hit called Mista Dobbelina.
This is the best sample that I can come up with. There are lots of rap songs in the pop charts, but these rappers I don't consider them underground. Underground hip hop is still that is packed with metaphores and heavy brag and boast raps. Also with a realistic message either it is political, social or economical. To me underground hip hop listners are a minority whom are looking for raw beats and lyrics. I am very aware of these rappers that who are playing a part is only out to make money.