Blu-Ray is an optical disc format designed to be the successor to DVD (and competitor to HD DVD). The new format is named for its use of blue laser to read information from Blu-Ray discs. The blue laser has a shorter wavelength of 405nm as opposed to the red laser used in CD and DVD that has a longer wavelength of 650nm.
Blu Ray can use the shorter wavelength for greater focus to read finer print etched onto media, more information can be stored to the disc than anything read by red laser technology. Despite the new laser, Blu-ray players promise to be fully backward compatible to the older CD and DVD formats. Discs using the new format will be capable of holding 25Gigs of data, double density versions of Blu-Ray have been announced capable of up to 50Gigs.