Image Resolution DPI vs PPI
It's always confused me about this stuff. I know what the monitor resolution means, it's spreading pixels (colored dots) across the monitor screen.
Dots per inch (DPI) usually refers to a printer and Pixels Per Inch (PPI) refer to computers, cameras and scanners.
Anyway, here is a good explanation about it.
http://www.scrapbook-bytes.com/cgi-script/tutorials/publish/printer_285.shtml