Pixels Per Inch (PPI) describes Image Resolution which refers to the Number of Pixels contained within Each Inch of a Digital Image.
A Higher Resolution/PPI Image contains More Pixels and is a Higher Quality of Image.
A Lower Resolution/PPI Image contains Less Pixels and is a Lower Quality of Image.
To Calculate PPI:
Number of pixels ÷ size of the image in inches = Pixels Per Inch.
Substitute 1 cm for 1 Inch to find Pixels Per Centimeter or PPcm2.