Blu-ray is an optical disk storage device capable of holding 25GB of information (or 50GB for dual layer discs), designed to replace the DVD format.
The main use of Blu-ray disks are for high definition movies or PS3 games.
Blu-ray was developed by a consortium that included Sony and Philips.
There was a competing high definition format—HD-DVD, developed by Toshiba. Blu-ray, however, has largely out-grown it and is largely considered the "winner" if the HD format wars.