Device pixel (Computing)
In the realm of computing, a device pixel refers to the physical pixel of a device's screen, that is, the precise outcome of the manufacturing process of the device's screen.
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The physical size of a device pixel varies across devices. For example, devices with retina screens (i.e. the iPhones, the iPads) tend to have much much smaller pixels than devices with regular screens. The result is that the smaller the pixels (in size), the more of them are required to fill up a given space, and thus the crisper the final, rendered image.
In web development, particularly when working with CSS, a device pixel is often contrasted with a CSS pixel, which is a unit of length (and is therefore the same across all kinds of devices).