DPI (dots per inch)
How many image pixels land in each printed inch. Aim for about 300 for sharp printed images.
DPI describes image resolution at the size an image prints. Divide an image's pixel width by its printed width in inches to find it.
Images around 300 DPI print sharp. Below about 150 they can look soft or blocky. Typing 300 into an image editor without adding pixels does not add detail.