Description taken from Project iM@S wiki:

THE IDOLM@STER BRILLIANT STARS is a general, non-specific title used for defining a group of idols from the six brands of THE iDOLM@STER series, THE iDOLM@STER, THE iDOLM@STER Cinderella Girls, THE iDOLM@STER Million Live!, THE iDOLM@STER SideM, THE iDOLM@STER Shiny Colors, and Gakuen iDOLM@STER. Read more on Last.fm. User-contributed text is available under the Creative Commons By-SA License; additional terms may apply.