High-definition, or HD, video refers to a digital video with a minimum resolution of 1280 by 720 pixels. In video technology, it is considered as third generation.
The first generation of video technology started with analog video before proceeding to standard definition, or SD, digital video. HD video is bigger in file size, screen size and resolution compared to the other two. It is not based on PAL or ASTC standard, unlike the other two.
There are three main types of HD video, 720p, 1080p and 1080i. The letter "i" stands for interlaced frame while "p" stands for progressive frame. Both 1080p and 1080i have a resolution of 1920 by 1080, while 720p has a resolution of 1280 by 720.