You don't know what blu-ray is?
Its a new type of disc that uses a blue laser to be read that has a shorter wavelength (405 nanometers) than a red laser (650 nanometers). The smaller beam focuses more precisely, enabling it to read information recorded in pits that are only 0.15 microns (Ám)
The discs as of now can store 25gb one sided, or 50gb dual layer, though discs are coming that can hold more than 200gb dual layer.
its fighting to be the next sucessor for DVD playing in high definintion, but I believe its main purpose should be for more computer backup as well.
It'll be used as the disc medium on the Sony PS3.