Taken from another website.
Also known as 4K, Ultra HD is the term most brands now use to describe TVs that carry the next generation of pixel resolution: 3840 x 2160.
If you know your HD onions you’ll realise that these numbers exactly double the 1920 x 1080 resolution of today’s full HD TVs. But this doesn’t just mean you get twice as many pixels; a bit of GCSE Maths will tell you that squeezing 3840 x 2160 pixels into a screen actually delivers four times as many pixels as you get with a full HD screen: a mind-boggling 8,294,400, to be precise.
This predictably has a pretty profound impact on picture quality. The most obvious point is that you can simply see far more detail in Ultra HD pictures than you can in full HD ones. But the much higher level of resolution also delivers smoother colour blends and a greater sense of depth, as details can be resolved further into the distance. Overall the extra pixels in Ultra HD TVs make it feel much more like you’re watching the real world through a window rather than looking at a picture being rendered by a TV screen