HDMI (High-Definition Multimedia Interface) is a compact audio/video interface for transmitting uncompressed digital data. It represents a digital alternative to consumer analog standards such as Radio Frequency (RF) coaxial cable, composite video, S-Video, SCART, component video, D-Terminal, and VGA. HDMI connects digital audio/video sources such as set-top boxes, Blu-ray Disc players, personal computers (PCs), video game consoles (such as the PlayStation 3 and Xbox 360), and AV receivers to compatible digital audio devices, computer monitors, and digital televisions.

HDMI supports, on a single HDMI cable, any TV or PC video format, including standard, enhanced, and high-definition video, up to 8 channels of digital audio, and a Consumer Electronics Control (CEC) connection. The CEC allows HDMI devices to control each other when necessary, and allows the user to operate multiple devices with one remote control handset. Because HDMI is electrically compatible with the signals used by Digital Visual Interface (DVI), no signal conversion needs to take place nor is there a loss of video quality when a DVI to HDMI adapter is used. As an uncompressed connection, HDMI is independent of the various digital television standards used by individual devices such as ATSC and DVB as these are encapsulations of compressed MPEG video streams (which can be decoded and output as an uncompressed video stream on HDMI). You can read more at the NY Times