4K resolution, also called 4K2K, refers to a display device or content having horizontal resolution on the order of 4,000 pixels. Several 4K resolutions exist in the fields of digital television and digital cinematography. In the movie projection industry, Digital Cinema Initiatives (DCI) is the dominant 4K standard.
4K has become the common name for ultra high definition television (UHDTV), although its resolution is only 3840 x 2160 (at a 16:9, or 1.78:1 aspect ratio), which is lower than the 4K industry standard of 4096 x 2160 (at a 19:10 or 1.9:1 aspect ratio).
The use of width to characterize the overall resolution marks a switch from the previous generation, high definition television, which categorized media according to the vertical dimension instead, such as 720p or 1080p. Under the previous convention, a 4K UHDTV would be equivalent to 2160p.