Refers to the concentration of pixels on a particular display, measured in pixels per inch (PPI). Pixel density is calculated by dividing the diagonal pixel resolution of a display by its diagonal size.
Pixel density has become increasingly important as the resolution of screens has increased dramatically in the past several years. For example, the Apple iPhone XR has a high resolution screen with a pixel density of 323. In contrast, older XGA monitors had a PPI of around 85. Increased PPI can improve the quality of the viewing experience. Even when held closely, high PPI screens do not look pixelated (assuming that the image is of high enough quality to begin with).