GNU is an operating system and an extensive collection of computer software. GNU is composed wholly of free software, most of which is licensed under the GNU Project’s own General Public License (GPL).
GNU is a recursive acronym for “GNU‘s Not Unix!”, chosen because GNU‘s design is Unix-like, but differs from Unix by being free software and containing no Unix code.
The GNU project includes an operating system kernel, GNU Hurd, which was the original focus of the Free Software Foundation (FSF). However, given the Hurd kernel’s status as not yet production-ready, non-GNU kernels, most popularly the Linux kernel, can also be used with GNU software. The combination of GNU and Linux has become ubiquitous to the point that the duo is often referred to as just “Linux” in short, or, less frequently, GNU/Linux.
Richard Stallman, founder of the GNU project
Richard Stallman, the founder of the project, views GNU as a “technical means to a social end”. Relatedly, Lawrence Lessig states in his introduction to the second edition of Stallman’s book Free Software, Free Society that in it Stallman has written about “the social aspects of software and how Free Software can create community and social justice”.