Pixels Per Inch, also referred as pixel density, refers to the number of individual pixels that a computer display in a single inch area. PPI can also describe the resolution of an image scanner or digital camera.
The apparent PPI of a computer monitor depends upon the screen resolution selected. A monitor set to 800 x 600 display resolution mode has a lower PPI than the same monitor in 1024 x 768 mode. Only the doth pitch of a computer display can determine the maximum limit of possible pixel density.