In the late 1960s, the term supergroup was coined to describe music groups comprising members of great proficiency who had already achieved fame or respect in other groups or as individual artists. The term took its name from the 1968 album Super Session with Al Kooper, Mike Bloomfield, and Stephen Stills. The coalition of Crosby, Stills and Nash (later Crosby, Stills, Nash and Young) is another example.
With the success of Cream, the term also came to include groups that sold huge numbers of albums and headlined massive concerts, regardless of the previous fame of the individual members. However, the term as correctly applied refers to the architecture, not the achievements, of the group. By any standards, it is not a rigidly defined category and has become, more than anything, a marketing term.
Supergroups tend to be short-lived (often lasting only for an album or two), perhaps because of the natural conflict of egos between established stars. Also, some supergroups were formed as side projects that were never intended to be permanent.
Demons and Wizards: formed by Hansi Kursch of Blind Guardian and Jon Schaffer of Iced Earth, this band combined the two other bands' influences and techniques, coming together to form beautiful power metal.
Led Zeppelin is a marginal case, because although Jimmy Page and John Paul Jones were famous and respected when the band formed as The New Yardbirds, the other half of the group were relative unknowns at the time (albeit very competent unknowns). Page's original intention for the group was to include other well known musicians for the vocalist and drummers spots.
XYZ, ex-Yes and Led Zeppelin members who became a true supergroup on creation, despite the group not surviving long enough to produce any official albums.
Other supergroups
Anderson Bruford Wakeman Howe is a strange case, because although all of the musicians were famous and respected, they were largely (but not entirely) so because of their earlier achievements together in Yes.
