Original: On January 4, 2008, a day before CES 2008, Warner Bros. (the only major studio still releasing movies in both HD DVD and Blu-ray Disc format) announced that it would release only in Blu-ray Disc after May 2008.
Simplified: Blu-ray Disc is a high-density optical disc format similar to DVD. Blu-ray is the type of disc used for Playstation 3 games and for playing high-definition (HD) movies.