Question

what is the full form of PPI

Answer 1

Pixels Per Inch is the full form of PPI

Answer 2

PPI is Pixels per Inch.  PPI is related to the resolution of images when they are printed on paper.  Usually high resolution is needed for good quality photographs.

50 PPI is low resolution. 300 ppi is a good resolution.

DPI is dots per Inch.  Usually there is one dot per pixel. There can be more pixels in one dot too.

The size of image file when saved on the hard disk changes when resolution is changed. The size increases for higher resolution.