An HDMI cable connects digital audio/video devices to each other so that data can be transmitted from one device to the other. For example, a DIRECTV receiver, DVD player, Blu-ray™ Disc player, or similar device, to an HDTV. It allows the transmission of both audio and video data over a single cable and it's a digital alternative to analog cables like S-Video, coaxial, composite video, or VGA.
HDMI cables are available at most electronics stores. To connect an HDMI cable from your HD DVR or HD receiver to your HDTV, just look for the port labeled "HDMI" on each device and insert the proper end of the cable into each of the ports.