Underground music is music which has developed a cult following, independent of commercial success. This music generally speaking has little or no mainstream appeal, visibility or commercial presence. The term is also currently used to describe contemporary music of non-mainstream musical exponents with actual specific genre or style being unimportant in determining the "underground" status. This diversity may serve to "protect" underground music from being packaged and marketed based on a restricted, easily identifiable sound.

The term underground music has been applied to several artistic movements, such as the psychedelic music movement of the mid 1960s, punk rock and hardcore, hip hop, alternative rock, grunge, various forms of heavy metal, electronica, outsider music, and experimental music, plus many more.

A music underground can also refer to the culture of underground music in a city and its accompanying performance venues. The Kitchen is an example of what was an important New York City underground music venue in the 1960s and 1970s.

"Underground format" is a term used to describe a type of music radio programming in which underground music is played, usually in long blocks of two to three hours at a time, keeping talk to a minimum. http://www.channel501.com/kmpx/index.html