Defined
High Definition Television (HDTV), is a set of screen resolutions for television sets defined by the Advanced Television Systems Committee, commonly used on Digital Television. It provides a superior quality picture to regular analog television as well as progressive scan output, by providing either 720 progressive scan lines, or 1080 scan lines (interlaced or progressive). The screen aspect is always 16:9.
What is HDTV?
A broadcast in HDTV must either:
An HDTV compatible display must support all these options.
How does it look?
Since HDTV uses at least 50% more scan lines, and a 16:9 aspet ratio, picture quality is much better, with increased sharpness, clarity, and detail.
In Practice
HDTV is available:
HDTVs ar offered as (in order of increasing price/quality) DLP (front- or rear-projection), Plasma, or LCD displays.