Simply put DPI means Dots per Inch. It works a lot like the resolution of a TV. The higher the DPI (or resolution) the better the picture.
For printing, this means the higher the DPI, the clearer and sharper the print will be.
At a minimum, we recommend 150 DPI for printing. Many of our materials are a fine weave, so the smallest detail will be visible.
Please see the images below for quick visuals of what you could expect with different DPI in photos. (Photo was taken with an iPhone 8+)
While it's difficult to see, it becomes more obvious once you zoom in.