Regular NTSC signals have 525 lines of resolution. HDTV has 1125 lines of resolution having over five times the video information than that of a conventional NTSC-type TV set. In spite of its obvious advantages, transmission requires extraordinary bandwidth of five times the capacity of a conventional TV signal. TV receivers are estimated to be 30% more expensive than today's most costly sets.
SOURCE :www.tamu.edu/ode/glossary.html

Short for high-definition television, one mode of operation of digital TV whereby the broadcaster transmits a wide-screen picture with many times more detail than is contained in current analog television pictures.
SOURCE :www.myetv.org/television/dtv/glossary.cfm

High-Definition Television. The high-resolution subset of our DTV system. The FCC has no official definition for HDTV. The ATSC defines HDTV as a 16:9 image with twice the horizontal and vertical resolution of our existing system, accompanied by 5.1 channels of Dolby Digital audio. The CEA defines HDTV as an image with 720 progressive or 1080 interlaced active (top to bottom) scan lines. 1280:720p and 1920:1080i are typically accepted as high-definition scan rates.
SOURCE : www.hometheatermag.com/glossary/

The generally agreed upon definition of HDTV is approximately twice the vertical and horizontal picture resolution of today's NTSC TV, which essentially makes the picture twice as sharp. HDTV also has a screen ratio of 16:9 as compared with most of today's TV screens, which have a screen ratio of 4:3. HDTV offers reduced motion artifacts (ie ghosting, dot crawl), and offers 5.1 independent channels of CD-quality stereo surround sound, (also referred to as AC-3).
www.hdtvinfoport.com/HDTV-Glossary.html

Analog: An analog TV cannot display progressive-scan DVD or HDTV. It can show only standard-definition programs such as those found on regular TV, cable, or satellite--including digital cable and DirecTV or Dish Network.

Digital: A digital television, sometimes called a DTV, can also display progressive-scan DVD and almost always HDTV.

EDTV: This stands for Enhanced-Definition TV, and usually it describes a television that can display HDTV signals but doesn't have enough resolution to really do them justice. Most often it applies to plasma TVs and denotes 852x480 pixels (more info).

HDTV: High-definition televisions, or HDTVs, can display standard TV, progressive-scan DVD, and HDTV signals. They're by far the most common type of digital television.

Resolution, or picture detail, is the main reason why HDTV programs look so good. The standard-definition programming most of us watch today has at most 480 visible lines of detail, whereas HDTV has as many as 1,080. HDTV looks sharper and clearer than regular TV by a wide margin, especially on big-screen televisions. It actually comes in two different resolutions, called 1080i and 720p. One is not necessarily better than the other; 1080i has more lines and pixels, but 720p is a progressive-scan format that should deliver a smoother image that stays sharper during motion (for more on progressive scanning, see our primer). Another format is also becoming more well-known: 1080p, which combines the superior resolution of 1080i with the progressive-scan smoothness of 720p. True 1080p content is extremely scarce however, and none of the major networks have announced 1080p broadcasts