H.264 is the International Telecommunications Union-Telecom (ITU-T) designation for one of its digital video codec compression standards. It takes a digital video stream and compresses it into a lower bit rate that makes it practical to transmit on existing broadband communications systems and media.
The ITU-T's Video Coding Experts Group worked with the Moving Picture Experts Group to produce a common video compression standard. H.264 is also designated as MPEG-4, Part 10 or just Advanced Video Coding (AVC) as an ISO/IEC standard. Technically, the standards are identical.
H.264 is widely used as the compression standard in Europe's Digital Video Broadcast (DVB) system. Also, it's a mandatory feature of the new HD DVD and Blue-ray digital video recorders. It's used in Japan's ISDB-T mobile terrestrial broadcast service and in virtually all direct broadcast satellite TV services as well.
The Advanced Television Systems Committee (ATSC), the U.S.'s HDTV standards organization, eventually may adopt it as one possible optional codec. H.264 also is at the core of most of the forthcoming cell-phone TV systems, like DVB-H.