Resolution, also known as DPI (Dots Per Inch) or PPI (Pixels Per Inch), can be described as the number of dots that fit horizontally and vertically into a one-inch space. Generally, the more dots per inch, the more detail captured and the sharper the resulting image.
How to check resolution ?
To see if your file has the proper resolution for printing in Photoshop, click on Image>Image Size. View the resolution section. The resolution should be set to 300 dpi.
How do I know if my resolution is good for print?
If your artwork appears pixelated beyond the 300% view in Acrobat, then this
is an indication that your file is low resolution. If your artwork appears crisp at 300%, then this is a good indication that your resolution is print ready.