The name Blu-ray Disc is derived from the blue-violet laser used to read and write this type of disc. Because of this shorter wavelength (405 nm), substantially more data can be stored on a Blu-ray Disc than on the common DVD format, which uses a red, 650 nm laser. In comparison to HD DVD, which also uses a blue laser, Blu-ray Disc has more information capacity per layer (currently 25 GB, but test media is up to 33 GB). Several manufacturers have released 50 GB recordable BDs and rewritable discs.<1>. All supporting studios have either already released or have announced release of movies on 50GB discs.
Blu-ray Disc is similar to PDD, another optical disc format developed by Sony (which has been available since 2004) but offering higher data transfer speeds. PDD was not intended for home video use and was aimed at business data archiving and backup. Blu-ray Disc is currently in a format war with rival format HD DVD.
http://en.wikipedia.org/wiki/Blue_ray_diskI'm glancing through this article and there is wayyyyy too much information! :)