Groupie,
Pictures on the screen are made up of small coloured squares called pixels. A measure of its resolution is therefore Pixels Per Inch (PPI)
Inkjet printers make up the colour of any pixel with small dots of a few basic colours (usually 3 or 5 + black) Printer resolution is therefore measured in Dots Per Inch (DPI)
Your printer will usually have a fixed resolution (in dpi) that it prints at.
The PPI that you set in photo-imaging siftware will usually set the final image size but may be over-ridden by other software settings in your computer or printer.