DPI stands for dots per inch, which refers to the small ink dots that come on paper during the printing process. The amount of these ink dots in one inch of paper is the number you get for your DPI. These little dots are important because they determine how well your file will print.
You may ask, how do they do that? The dots per inch determine this based on another small number known as PPI or pixels per inch. To make sure your file prints in a high resolution you need to make sure that your dots per inch are larger than your pixels per inch. An example would be having a DPI of 1200 and a PPI of 300, leaving you with 4 ink dots for every pixel.
Finding out what the DPI of your image is can seem like a difficult task but is actually quite easy! If you are using a Mac computer, you simply open up the file in preview, click tools > Show Inspector. To resize on a Mac open the image or file in preview click tools> adjust size. If you are working in Windows, you want to open the image or file in the picture viewer on your computer. Once opened you will right click the file, then select “properties”, after that click on the “summary” tab. If “title”, “subject”, or “author” fields are displayed click “Advanced>>” on the bottom.