What is the meaning of Photostat?

A photocopy, especially one made by a Photostat machine.

A photocopy made using a photocopier.

Positive (black on white) or negative (white on black) reproduction of printed matter or artwork made on a photostat machine, which uses photographic paper instead of a transparent negative, and uses a prism to render the paper negative readable instead of reversed.

To make such a photocopy of.

photocopy

Source: wiktionary.org