The Full form of HD is High Definition. HD is basically the quality of image you will see on electronic devices of the images and videos. The electronic device’s screen i.e. television, mobile, laptop etc. has to display various videos and images but the quality of those files depends on the resolution. HD picture or video refers to any picture or video system of higher resolution than SD (Standard-Definition) video, and most commonly involves display resolutions of 1920×1080 pixels (1080i/1080p) or 1280×720 pixels (720p).
HDTV (High Definition Television) is a television display technology that provides a substantially higher resolution than that of a SD (Standard Definition) television. While there is no standardized definition or meaning for HD, but generally any video image with considerably more than 576 vertical lines in Europe and 480 vertical scan lines in North America is considered HD (High-Definition). 480 scan lines is considered as the minimum even though the majority of technology or systems greatly exceed that.
In some contexts, the images of standard resolution captured at rates faster than 50 frames / second in Europe and 60 fps in North America by a high-speed camera is considered high-definition. Some television series that are shot on high-definition video look as if they have been shot on film, a technique known as filmizing.