DCI 4K has twice the resolution of 2048 x 1080 pixels of projectors (4096 x 2160 / approx. 17: 9) and is the 4K resolution of the film industry. UHD 4K (also called UHDTV 4K), on the other hand, is the 4K resolution of the television industry, which was defined by the International Telecommunication Union (ITU). It has twice the horizontal resolution of 1920 x 1080 pixels Full HD (3840 x 2160/16: 9). 4K is a high resolution with twice the vertical and horizontal pixels of Full HD and refers to resolutions with a horizontal number of pixels of around 4 Millions.

As the screen resolution  continues to grow, pixel density is a new element that should be considered when choosing a display today. Pixel density in displays is a specification that indicates the level of resolution, and the value is usually given in ppi. Ppi stands for "pixels per inch" (not per square inch). One inch is 2.54 centimeters.
If you decrease the pixel pitch (pixel pitch) without changing the screen size of the LCD, the ppi will increase, and the higher this value, the higher the resolution of the display. For example, at 100 ppi there are 100 pixels per 2.54 centimeters, and at 300 ppi, 300 pixels are packed the same width.

DPR, or device pixel ratio, check here: Screen resolution, also known as CSS pixel ratio, is the number of physical pixels that make up a CSS pixel in any direction of a screen such as the width direction or the height direction.

It is difficult to describe, but if you compare the display of smartphones, on which displays with high pixel density are common, with those of conventional PC displays with low pixel density, you immediately see the advantage.