“Ultra high definition is also known as Ultra HD, UHD, and UHDTV. In Japan, 8K UHDTV will be known as Super Hi-Vision since Hi-Vision was the term used in Japan for HDTV.” – Ultra high definition television, Wikipedia
4K UHDTV [ or 4k TV. Or Ultra High Def TV ] (2160p) is 3840 pixels wide by 2160 pixels tall (8.3 megapixels), which is four times more pixels than 1920 × 1080 (2.1 megapixels).
8K UHDTV (4320p) is 7680 pixels wide by 4320 pixels tall (33.2 megapixels), which is sixteen times more pixels than current 1080p HDTV