Blu-ray Disc is an optical disc storage media format and is used like its predecessors (CDR and DVD) for storing data and video.
The name Blu-ray is derived from the blue laser used in the machine. Because of its shorter wavelength (405nm), more data can be stored on a Blu-ray Disc than on a DVD which uses a red (650nm) laser.
As with Betamax and VHS, Blu ray has beaten its competitor HD DVD, which was launched at a similar date.
Because the Blu-ray Disc data layer is closer to the surface of the disc, compared to a DVD, they were housed in cartridges for protection. They no longer have cartridges due to the advances in polymer technology.