overground
It being related to music is the only correct part of the last definition. A level reached by few, overground is when an underground artist becomes so popular that they can no longer be called underground. I would say that any underground artist who sells 1 mill+ copies of any one of their albums can be considered overground.
Synonyms for overground
On this page, you will find 30 slang terms related to overground. Some of the top words include: Tap dat Ass, Armin van Buuren, superb, blingity, deep, and 25 more.