PostScript is a page description language developed by Adobe Systems. It is a language for printing documents on laser printer, but it can also be used to produce images on other types of devices.
Showpage command transfers the contents of the current page to the current output device.
The main function of showpage is
It executes the endpage procedure in the page device dictionary
• Executes the function equivalent of an initgraphics operation, reinitializing the graphics state for the next page
• In page device dictionary, it executes the beginpage
• If the Boolean result returned by the EndPage process is true, transmits the contents of the page to the current output device and performs the equivalent of an erasepage operation, clearing the contents in preparation for the next page.