underground
underground is like deeper beats, lyrics and soul to a song - commercial is like what get's played on the radio and is marketed to the masses - Britney's mainstream, Eminem is mainstream - even though anyone can make underground music they don't coz it doesn't sell like commercial stuff - underground IS deeper, more hardcore, more controversial, or whatever...
sup the chenist - dust c.d is underground.. you'll know the difference if you know your music...

NB: It isn't underground because it hasn't hit mainstream yet - it's whole design is different to mass appeal.