The Gnu Philosophy
 What the GNU?
GNU is a recursive acronym that stands for GNU's Not Unix. The GNU Project was started by Richard Stallman in the 1980's to create a completely free operating system for everyone to use, share, and modify. The GNU philosophy revolves around free software.
 What is Free Software?
From the GNU Project website:
|Free software is a matter of liberty, not price. To understand the concept, you should think of free as in free speech, not as in free beer.
Free software is a matter of the users' freedom to run, copy, distribute, study, change and improve the software. More precisely, it refers to four kinds of freedom, for the users of the software:
 Is This Like Open Source?
Yes, however while using similar means the projects have fundamentally different goals. The GNU Project is about freedom for users and developers, while the open source movement is about having source code available (and many licenses included with said source code do not let you modify and redistribute the code).