Ultra HD TV, also referred to as 4k, UHD, Ultra HD, and sometimes Quad HD, is a video format with a resolution of 3840 x 2160 (8.3 megapixels) that is 4-times the Full HD standard of 1920 x 1080p (2.1 megapixels). Current HDTV standards also fall into two lower video resolutions that include 720p and 1080i, but those formats contain either fewer lines of resolution (720p) or are interlaced rather than progressive (1080i).
4k Ultra HD resolution was defined on Oct. 17, 2012 when the CEA (Consumer Electronics Association) announced the term Ultra HD (Ultra High Definition) would be used for displays with a video resolution of 3840 x 2160. But in most cases, consumer electronics manufacturers refer to Ultra HD sets also as 4k TVs, as the term is used more widely to describe the technology.
It’s interesting to note that in film 4k has a slightly different definition for 4k. The Digital Cinema Initiatives (DCI) established the SMPTE 428-1 standard that defines several 4k resolutions that include 4096 × 2160 (full frame), 3996 × 2160 (flat crop), 4096 × 1716 (CinemaScope crop) all with slightlhy different aspect ratios.
The next jump in video resolution is 8k UHDTV at 7680 x 4320 (33.2 megapixels) which is 16-times the current HDTV standard. See 4k/8k TVs on Amazon
Here is a chart that illustrates the different format sizes.