GNU

GNU (pronounced "guh-noo") is a recursive acronym that stands for GNU's Not Unix. It is a project to develop a feature-complete implementation of a Unix-like system, whose source code would be completely Free. Many of the GNU system's core tools are used by Linux; this has led some people (notably Richard Stallman and the Debian project) to refer to the system as "GNU/Linux".

One of the most important contributions of the GNU project is not software, but a license for distributing free software: the GNU GPL or General Public License. The Linux kernel is released under this license, as is much of the crucial software in any Linux distribution.