A High Definition TV also known as a 720p display, is the current standard for Entry Level Televisions, HD or 720p refers to a display with a resolution of 1280x720 pixels. The higher the resolution or the higher the number of pixels, the sharper the image quality is.
Full High Definition Televisions also referred to as 1080p displays, are a display with a resolution of 1920x1080, that is just over 2 Million pixels and more than twice that of HD or 720p. Thus giving a sharper image quality.
Ultra High Definition Televisions or UHD TVs are also referred to as 4K Television, the 4K name is derived from a horizontal resolution of approximately 4,000 Pixels, this can sometimes be 3840x2160 or 4096 x 2160, this gives a UHD Television a resolution of anywhere from 8.2Million to 8.8Million Pixels, Resulting in an extremely fine image allowing bigger screens to be viewed from closer distances without images appearing distorted.