The GNU project is a mass collaborative initiative for the development of free software. Richard Stallman founded the project in 1978 at MIT.
The original purpose of the GNU project was the creation of a free operating system. Free, in a software context, does not necessarily mean free of cost. The freedom referred to is the ability of anyone who wishes to run, copy, distribute, study, change and improve the 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.
Richard Stallman announced the GNU Linux project in 1983 and cofounded the Free Software Foundation in 1985. The GNU Linux project was started to create a Unix-like operating system created with source code that could be copied, modified, and redistributed. Those stipulations are an implementation of Stallman’s copyleft concept, a derivative of copyright law that serves "the opposite of its usual purpose: instead of a means of privatizing software, it becomes a means of keeping software free." Hence the slogan, “Copyleft: All rights reversed.”
According to the GNU Linux project, the Linux operating system's kernel is Linux but all other elements of the system are GNU. According to the project, neither OS exists independently and, as such Linux would more appropriately be called GNU Linux.
GNU stands for GNU's not Unix, often said to be the first recursive acronym (an acronym in which one of the letters stands for the acronym itself).