DPI or PPI? Which to use?

[Francis S]

Hi!

I was reading about DPI/PPI, learnt about it in school... graphic design. They say DPI is only for printing. That on web we use PPI. But everyone say DPI for web design, which if i understand right doesn't make any sens since its for printing! And they say DPI for Mouses's sensibility! Is that the same thing? Why do people say DPI for other than printing, on computer, if its supposed to be only printing?

And does the dpi/ppi REALLY matter for web design? Why? In what?

I greatly appreciate any explanation!