is an operating system platform that was developed in the late 1960's by people at AT&T Bell Labs, and is very strongly organized for networking and server use. The history of Unix is rather complicated, and many different companies have put out different proprietary versions over the years, sometimes with very large differences between them, but all sharing the same overall archetectural design.
The GNU project
was started by Richard Stallman as a reaction against the proprietary nature of most software. He was determined to develop a set of FREE software tools, and eventually an entirely free Unix-compatible computing system. He and other volunteers evenually succeeded in developing an almost-complete set of administration and complilation tools, but were lacking in one important detail, a FREE and useful unix kernel (the central underlying core component of an operating system that does all of the lowest level work).
In 1991, a gifted computer student in Finland, Linus Torvalds, decided he wanted to learn how to use Unix. But the existing unixes of the time were all too expensive. So he sat down and wrote his own instead. He developed a working kernel and basic file-system tools, and released them onto the networks under the GPL license. It was quickly combined with the GNU tools and together they became the popular "Linux
" platform we know today (and yes, GNU/Linux is probably the more accurate term, since the GNU project is as, or even more important than, the kernel itself).