A prepress proof is an analog or digital proof that uses inkjet, toner, dyes, overlays, photographic, film, or other techniques to give a close approximation of what the finished piece will look like. Unlike a press proof, the prepress proof does not use the actual printing inks therefore color proofs may not be quite as accurate as a press proof.
Analog prepress proofs include inexpensive contact proofs, such as bluelines, used for checking positioning or where exact color is less critical; and, more expensive but increasingly accurate color overlay and laminate proofs.
When all your printing is done to your desktop printer there is little differentiation between any proof copies you print although you might refer to the final proof you print when you feel everything is ready as the prepress proof. It may be printed at full print quality (as opposed to draft or ink-saver mode) on the final paper and is used as a final check that everything will print correctly before loading the paper tray and setting a larger print quantity.