A person who considers themselves a huge fan of a certain band, mostly to the point of purchasing the band's merchandise and attending their concerts, despite only knowing one of their songs, most of the time being the band's most mainstream hit.
One Song Fan: "Oh my god!!!! I'm the biggest fan of AFI!!! They rock!!! I wanna see them live!!!"
Friend: "Ok cool. What's your fave AFI song?"
One Song Fan: "Miss Murder. But that's the only song I've heard from them. But they ROCK!!! I love them!!!"
A band or singer who alters their original style of music in order to appeal to a wider audience and to make more revenue for their music, sometimes promoting it to various forms of media, including radio and advertisements.
Examples of bands and singers considered sell outs:
Fall Out Boy