A GPL license is when you obtain a copyrighted work as in a Ghostscript. A Ghostscript is the name of a set of various software. A GNU is a general license for free software.
The GNU General Public License, often shortened to GNU GPL (or simply GPL), lists terms and conditions for copying, modifying and distributing free software. The GPL was created by Richard Stallman in order to protect GNU software from being made proprietary. It is a specific implementation of his "copyleft" concept. According to Stallman, copyleft is a derivative of copyright
And once again, a copyright-related question posted on the copywriting forum. Definition for both terms have been posted many times, and there is a sticky thread clarifying the difference but let's refresh these concepts, COPYWRITING COPYRIGHT Copyright related issues are discussed (and should be posted) here,http://forums.digitalpoint.com/forumdisplay.php?f=44