Ghostscript is an interpreter for PostScript™ and Portable Document Format (PDF) files. It is available both under the GNU GPL license and for commercial licensing from Artifex. It has been under active development for over 20 years and has been ported to many different systems during this time.
Ghostscript consists of a PostScript interpreter layer, and a graphics library. Sometimes the Ghostscript graphics library is confusingly also referred to simply as Ghostscript. Even more confusingly, sometimes people say Ghostscript when they really mean GhostPDL.