No, 4K is called 4K because 4K is based on cinematic definitions, while the older resolutions are based on TV definitions. For TV you count the height, as that

No, 4K is called 4K because 4K is based on cinematic definitions, while the older resolutions are based on TV definitions. For TV you count the height, as that's the only thing that matters — you can always add more high-frequency signal to increase the width after all. That's why TV signals for e.g. DVD also use a 480p signal for 4:3 and 16:9, you just stretch the content, no problem on analog TV. (In fact, the "p" doesn't mean pixels, it means the content isn't interlaced (progressive) while 1080i would be interlaced content, with both 540p and 1080i having the same amount of lines per frame) While for cinema you count the width, e.g. what's more commonly known as 1080p is just 2K in cinema terms, as it's 1920 (or roughly 2048) wide. And that's why 4K is 4K, as cinema content is actually rendered in 4096 pixels width. In cinemas you can always add or remove height (just don't project onto that part of the screen, some cinemas even have screens able to change their height), while the width is fixed (you usually can't make the screen wider). Historically this also held true with film: except for IMAX (70mm portrait), you measure the width of the film e.g. 8mm, 16mm, 35mm, 70mm, as you can always just make the film longer to change the height. It's true that manufacturers quickly started calling their UHD content 4K for marketing reasons, but 4K doesn't have anything to do with your hypothesis. Now why was it used as marketing term? When HD and Full HD rolled out for consumers, cinemas started upgrading their projectors as well, offering content in 4K, and advertising it as such. Consumers got used to 4K meaning high resolution high quality. And when consumer devices started reaching a similar quality, obviously the manufacturers used the already established term, instead of the official "UHD" branding.