Stands for "High Definition Television". A kick ass video format with resolutions of 720p (1280x720 pixels progressive), 1080i (1920x1080 pixels interlaced) and 1080p (1920x1080 pixels progressive). Can be up to 6 times the quality of standard definition video. Using a proper HDTV (not an EDTV) viewing medium, it can be as good as looking through a window.
If you cannot get high definition television channels in your area, purchase a WMV HD DVD. Visit www.wmvhd.com for more info.
Stands for High Definition TeleVision. Widely believed to be anything better than SDTV, however, that is not the case. HDTV and SDTV are infinitely the same and HDTV only beats it out slightly on things like sharpness and MAYBE color. If you honestly can see a difference your brain is playing some serious tricks on you and is basing itself on the facts that everyone else thinks it looks better, so that's obviously the case. It's not.
I bought a HDTV, unfortunately, the quality I was getting when properly hooked up to a HDTV feed was so minimal a change in comparison to my old SDTV, that I exchanged it for my sixteen hundred dollars back.