Ghostscript can be used as:

A.
A Line Printer Daemon

B.
A print filter to convert PostScript data for non-PostScript printers

C.
A print filter to allow correct printing on PostScript printers

D.
A print filter to remove "ghosting" and "staircase" effect problems

E.
A graphical viewer for PostScript files

Explanation:
From http://www.ghostscript.com/Ghostscript.html:
Ghostscript is a package of software that provides:
* An interpreter for the PostScript (TM) language, with the ability to convert PostScript language files to many raster formats, view them on displays, and print them on printers that don’t have PostScript language capability built in;