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.