Richard Stallman is the founder of the FSF and the creator of the GNU General Public License. One of the purposes of the FSF is to promote and develop free alternatives to proprietary software. The GNU project is an effort to create a free Unix-like operating system from scratch and was started in 1984.
GNU represents this free software licensed under the GNU General Public License. GNU software is software designed to meet a higher set of standards than its proprietary counterparts.
GNU has also become a movement in the computing world. When the word GNU is mentioned, it usually evokes feelings of extreme left wing genius's who produce free software in their spare time that is far superior to anything even large corporations can come up with through years of dedicated development. It also means distributed and open development, consistency, compatibility and technical cutting edge information technology. GNU means doing things once in the best way possible, providing solutions instead of quick fixes, and looking exhaustively at possibilities instead of going for the most brightly coloured expedient approach.