Success/fame or any other kind of personal gain at the cost of credibility; and ANYBODY could be a sellout not just a musician/band. There's things that you get naturally and there's things that require selling out to have. And what sucks more is that you can't go back after you did it.
I don't want to name names so I can't give an example of selling out.
by C.F.C. October 29, 2007
To compromise one's values and/or aristic vision in order to gain fame and/or monetary profit. Commonplace in today's musical society. It is rare to find a successful musical artist who has not "sold out", however, this is not to say that they do not exist.
Good Charlotte never sold out. Selling out requires having some artistic vision in the first place.
by Dani.Havok.Kidd August 11, 2003
A band has “sold out” when their fans no longer get feel like part of an elite clique. This generally happens when a band attracts interest from a major label, who provides them with a higher recording budget, which results in just enough polish to make the band acceptable to a slightly wider audience; unfortunately, the better production generally reveals the band’s basic lack of musical talent, which hipsters could previously not see because it was hidden behind a blurry cloud of “lo-fi.”. What hipsters once assumed were “fractured pop songs” are revealed to simply be “bad pop songs,” and the hipsters aren’t smart enough to figure out why their favorite band suddenly seems to suck way more than before, so they blame it on “commercial production” and this mysterious and ephemeral force of “selling out.”

Dr. David Thorpe
Hipster: Selling out to the corporate machine! Ahhhhhhhhh.
by M-Sauce July 28, 2006
unfortunately MetallicA, once the gods of metal decided to sell out. that pisses me off. the Metalligod has failed. WHY!!!!!st. anger suck.
kill 'em all kicks ass
master of puppets kicks ass
ride the lightning kick ass
...and justice for all kicks ass
the black album.......
st. anger sucks
by MetallilbangeR April 5, 2005
Anyone who sacrifices artistic integrity in an effort to become more successful or popular (generally in music); someone who forgets their roots.
by Sean Piece August 4, 2003
A human being who abandons their convictions to impress people and or become more popular.
Kelli got drunk just so her friends would think she was cool, what a sell-out.
by Hugh G. Wection November 13, 2004
One who betrays a cause for personal advancement.

The popular definition of sell out allows it to be used as an insult towards anyone in show business. On the contrary, there are many bands which are considered sellouts which are not.

For instance, Green Day. They are considered sell-outs because they are a punk band who was popular on MTV. Green Day never stated that they would never be on MTV, thus they are not sell-outs in that sense. They never changed their musical style for monetary reasons, thus they are are not sell-outs in the more literal sense of the word. If Fugazi were to sign up with Sony records, they would be selling out because they preach against major labels.
by SpinSpyder June 25, 2003