The abbreviation dpi stands for dots p'er i'nch (one inch corresponds to a length of 25,4mm) and describes the dot density that is a measure for the image reproduction quality. The higher this type of resolution, the more dots (pixels) an image has and the sharper and more accurate the image will be. The specification dpi is used for the resolution specification of printer, monitore, as well as digital and video cameras.
With a printer resolution of 300 dpi 300 dots come thus on the length 25.4mm.
The standard resolution (image resolution) of the display on the PC monitor is usually 72 dpi or 96 dpi. This value does not say anything about the resolution of the monitor itself. By changing the monitor resolution, the fixed standard image resolution makes the display of texts and images appear smaller at high monitor resolutions and larger at low monitor resolutions.