HDMI - (High Definition Multimedia Interface) A special plug and socket designed for high definition TV and video. Sometimes called the 'Digital Scart' it can carry both high definition quality audio and video signals. It's release has not been without some major bumps and the specifications for it have changed several times

HDMI originated as a Hollywood-approved video interface and an alternative to the less secure IEEE 1394. Unlike 1394, HDMI cannot be used for recording. Studios and TV makers were both heavily involved in the creation of HDMI.
All versions of HDMI, starting with 1.0, carry video to feed a display and stereo audio to feed TV speakers. Version 1.1 adds support for the nearly defunct DVD-Audio format. Version 1.2 supports the Super Audio CD. Version 1.2a brings the convenience of CEC (Consumer Electronic Control) which simplifies an a/v system’s operation by allowing components to talk to one another. Version 1.3--a very big deal--supports superior color palettes and lossless surround formats delivered via Blu-ray or HD DVD. Let’s discuss the latter in more depth.
Surround via HDMI
The following is an extreme but necessary oversimplification. Only HDMI 1.3 carries all known surround formats between a disc player and receiver at full resolution. That includes new lossless formats supported by Blu-ray and HD DVD, such as Dolby TrueHD and DTS-HD Master Audio. So if you’re buying a surround receiver, make sure it’s got HDMI 1.3. But there is a workaround. Most Blu-ray and HD DVD players have built-in surround decoders. Connect their multi-channel analog outputs to your receiver’s multi-channel analog inputs and you’re in business.
Copy protection
HDMI and DVI both support copy protection known as HDCP (High-bandwidth Digital Content Protection). The set and sources perform a handshake. If a device is not HDCP-compliant, the TV will not display a picture. This is a problem with some DVI equipment.