What is HDMI ?  Not an inkling. I do not know what is it until I watched this video.

HDMI Digital Video Home Theater Connections 

HDMI (High-Definition Multimedia Interface) is the latest and greatest digital audio/video cable connection and can give you great HDTV resolution. Besides HDTVs, HDMI is being included in a variety of devices these days, including DVD players, cable and satellite set-top boxes, Media Center Edition PCs, and the Sony PlayStation 3 gaming console.

What’s so great about HDMI? It’s all-digital, high-bandwidth, supports all variants of HDTV and carry up to eight channels of digital audio.  HDMI is also fully backward compatible with DVI.

HDMI cables don’t have to be super-expensive. In fact, certified HDMI cables can be relatively cheap, and there are many good online sources.

If you’re shopping for a new TV, a new receiver, or a new DVD player, or choosing an HDTV set-top box or satellite receiver, go with HDMI if you can. HDMI can provide the highest quality video signal and throws your multichannel surround sound audio in on the same cable. You really can’t go wrong here.

Source:  Home Theater For Dummies, 2nd Edition