High Definition (HD)
High Definition (or HD) refers to video that is of higher resolution and quality than standard-definition video. The definition of video, in general, refers to the number of pixels in a given display. A pixel is the smallest visible element on a display. With HD video, there are more pixels packed into a display, producing a sharper, cleaner image.
Video images with more than 480 horizontal lines in North America or 576 horizontal lines in Europe are accepted as high definition. In general, 480 scan lines is the minimum for high definition video even though the majority of systems greatly exceed that.
In some contexts, standard-resolution images captured at rates faster than normal by a high speed camera can be considered high definition. These capture rates are typically 60 fps in North America and 50 fps in Europe. Today, we have many forms of high definition video, including 720p HD and 1080p. Anything beyond 1080p, such as 4K would be categorized as Ultra HD.