Resolution describes the level of detail present in a digital format. High resolution is generally considered more visually pleasing as the pixels are not visible. Low resolution images and devices PPI refers to "pixels per inch" and DPI refers to "dots per inch." While technically different, the two are often used interchangeably. PPI is a measurement of how many pixels are present within a given inch of a digital device or image. For example, 100 ppi means that there are one hundred pixels in one inch while 300 ppi means that there are 300 pixels in one inch.
See also: PPI/DPI