what is hd ? Answer here

[Vikram]

HD is defined primarily by video resolution, which is higher than traditional television broadcasts. It provides for between one and two million pixels per frame that is roughly five times that of standard definition television. However, high definition is not defined by only one set of specifications; it is instead a family of video characteristics. HD referred to a video signal that consisted of 720 horizontal lines from top to bottom and 1280 vertical lines from side to side. Compare this to the 480 horizontal lines you find on a conventional DVD movie. Obviously, the greater the number of lines of resolution, the greater is the amount of detail that can be captured and display. HD has now come to encompass one more resolution option: 1080 vertical lines and 1920 lines of horizontal resolution.
HD is also defined by the video frame rate—this includes 23.98, 24, 29.97, 30, 59.94, and 60 frames per second. The frame rate chosen depends upon the video standard used—either PAL or NTSC. Next, you will come across another video term—progressive scan or interlaced scan. This is referred to with either a ‘p’ or an ‘i’ respectively written after the numeric resolution value. Progressive scan implies that the video frame on your screen is created by sequentially ‘drawing’ one scan line after another. On the other hand, an interlaced picture is created by first drawing all even numbered lines, and then interleaving the odd numbered lines on the screen.