Dots per inch
Dots per inch is a unit of measurement used mainly for screens and printers. Note: one inch is exactly 2.54 cm.
The more dots per inch, the higher the image resolution. Smaller details can be seen.
For example a standard screen can display 75 pixels per inch, whereas a printer can print at least 300 dots per inch on the paper. This explains why an image that looks good on the screen may be of lower quality once it is printed.
The difference between Dots and Pixels per inch is that the printer has to place several dots to print a pixel.