DPI may refer to any of the following:
1. Short for dot per inch, DPI is a measurement of printer resolution indicating how many ink dots the printer can place in one square inch, the higher the DPI the sharper the image. Therefore, a printer with 600 DPI is a printer that prints 600 x 600 per square inch or 360,000 dots per inch. Because all printers print using dots, printers with a low DPI may encounter jaggies. Resolution Enhancement and other edge enhancements help correct the appearance of jaggies with printers that support this technology.
When working with graphics only meant for a computer screen, 72 DPI is sufficient. Any graphics you intend to print should be at least 300 DPI.
2. DPI, or dots per inch, is also used to determine an image resolution.
When scanning an image you intend to send over e-mail or only intend to have viewed electronically, scan the image as 72 DPI to keep the image size small.