Pixels (px) are the smallest physical squares we find on digital screens. These are addressable, and we can define their color in an image or an application. As we now have devices with different concentrations of pixels per inch, if we define our assets with reference to these pixels, the icons or elements we design will be rendered in very different sizes according to the screen where they are displayed. A 24x24 px icon will be the correct size on a mobile with a low-density screen, but will appear very small when displayed on a mobile with a high-resolution screen.
If a file is not created taking into consideration the size at which it will be displayed, or if it is scaled in the rendering process, ...