It is the measure of how many dots of ink or toner a printer can place within an inch (or cm).
Most printers print the same number of dots horizontally and vertically, though some may have differing numbers. Basically, 300 dpi printers print 300 tiny little dots across one inch and 300 dots vertically for one inch
The term dpi (dots per inch) is relevant only when printing.
In printing, dpi is the measure of printed image quality on the paper.
Pixel dimensions are relevant to all images displayed on a computer.
This is sometimes called ppi or pixels per inch. A high-resolution monitor setting will display more pixels per inch.
soooooo Basically the term DPI refers to the resolution of the printing device, where PPI refers to the resolution of the image itself
Even though "dots per inch" (DPI) and "pixels per inch" (PPI) are used interchangeably by many, they are not the same thing.
Pixels per inch (PPI) refer to the square pixels in a digital image, which are in contact with the adjacent pixels.
There is no space between the pixels. The PPI is the display resolution - not the image resolution.
A simple example:
If you have an image that consists of only 1 green pixel. That's it. The whole image is one pixel big - 1 PPI
Then you print it on a printer that doesn't have a green ink cartridge, but it has blue and yellow.
The printer will then print one blue dot, and one yellow dot in order to get a green dot. So, your file was 1 PPI, but the printer had to print 2 DPI to render it correctly.
now that your brain is screaming for mercy the reason why the ppi images change size when you change the dpi is.....cos they can...no thats not it *slaps self* lol ....it's because no many how big or small you make the dpi the image will automatically change to having it's original quota of ppi - clear as mud huh