Blu-ray is a type of optical disc used for storing data. In the same way the DVD was meant to replace the CD-ROM, Blu-ray was meant to replace the DVD as the standard form of optical media. It has the same dimensions as those two aforementioned formats, but a much greater storage capacity.
Blu-ray discs require a 405 nm light to read data. As this literally "blue" light is much more dense than the red light used for DVDs, it allows for finer grooves to be made and read in discs. As a result, Blu-ray discs can store 25 GB per layer, compared to the less than 5 GB of the standard DVD.
Blu-ray was developed by a number of companies in a collaborative process, including Sony. The original prototype discs were first unveiled to the public in 2000, and the name "Blu-ray" was made official in 2002. However, unlike the DVD, Blu-ray took a while to become adopted. The exact specifications of Blu-ray would not be completed until 2004, and the first Blu-ray players were introduced to the market in late 2006 and early 2007.
Even when Blu-ray hit the market, it took some time for it to become a major format. This was due in part to competition from "HD-DVD" technology developed by Toshiba. Though HD-DVD lacked the capacity of Blu-ray, its lower costs made for some fierce competition. Toshiba would only concede defeat in 2009, after the two formats competed for a few years.
Even accounting for competition from HD-DVD, Blu-ray had a harder time being accepted by consumers than DVD did in the 90's and 2000's. This was partially due to the low number of HDTV's in the mid to late 2000's, which made Blu-ray's higher resolution movies pointless for many consumers. Blu-ray also faces competition from digital distribution of media, particularly "movies on demand" services such as Netflix, which require less expensive and more common hardware to run than Blu-ray discs and can be cheaper for certain groups of consumers.
Use in Game Consoles
Blu-ray technology was eagerly adopted by both Sega and Nintendo for their eighth generation consoles, the Eclipse and the Stream. These discs allowed for much larger, detailed, and complex games than the DVD. However, neither console is equipped to play Blu-ray movies, though hackers have successfully modified both consoles to do so. The lack of movie-disc functionality is part of an ongoing trend of sacrificing functionality in consoles to keep prices cheap.