You have probably heard this term many times before especially in the context of printing your digital photos. DPI is sometimes used as a measurement of digital photo printing quality while the truth is that DPI is an indicator of the printer quality.
DPI stands for Dots per Inch. DPI is a physical characteristic of a printer. Every printer prints dots that when put next to each other comprise a photo. Each dot has a physical size. DPI is also known as the maximum resolution that a printer is capable of. Low-end printers have lower DPI while high-end printers have higher DPI. DPI is defined as the number of dots a printer can print per inch. For example if a printer supports 1200 DPI it means that the printer can print 1200 dots per inch (on both X or Y axis). When printing it is important to make sure that the DPI is higher or equal to the number of pixels per inch in the source photo. If the DPI is lower the printer will not be able to fully display the high resolution photo. When the DPI is higher the printer will use multiple dots to represent one photo pixel. DPI is not relative to the page size. DPI is a fixed number for a given printer.