Learn in the textbookFundamentals of Color and Image Representation
Definitionppi (pixels per inch) is a unit of resolution expressed as the number of pixels lined up across one inch.
ExplanationA pixel is the smallest unit that makes up a digital image, and ppi is mainly used to describe how fine a display or smartphone screen is. Even on screens of the same size, a higher ppi makes the outlines of text and photos look smoother.
AnalogyIt is like tiling a wall of fixed size: the smaller the tiles and the more of them you use, the finer the pattern they can form.