4K simply means better video quality. Its horizontal resolution will be 3840 (or 4096) pixels. Also, the vertical resolution will be 2160 pixels.
This simply means that the higher the pixels of your screen, the better picture quality you will get.

It can also be understood in easy language that 4K display has 4 times more pixels than full HD display. That is, a 4K display is made by combining 4 full HD displays. Now technically, 4K has two main standards.

The first is DCI 4K resolution with a pixel resolution of 4096 × 2160. It is mostly used in the film and video production industry. Its resolution is twice that of DCI 2K. The second is UHD-1.

It can also be called ultra-high-definition television (UHDTV). Its resolution is 3840×2160. This technology is used in television and video games. A lot will become clear to you from the photo given below.