Unix is a mainframe operating system that was invented at Bell Labs in 1969. Linux is actually a free software (also known as open source) version of the Unix kernel, rewritten from scratch for the 'PC' (x86) hardware standards, with all the improvements that Linus Torvalds felt were needed. The Linux kernel plus the GNU software, creates the base system of what people generally refer to as 'Linux'. Add XWindows and a window manager like GNOME or KDE, and you get desktop 'Linux'.

Linux is one example of "copyleft" software, a concept introduced by Richard Stallman, founder of the GNU project, and the Free Software Foundation. Like copyright, copyleft means no one else can copyright and own a piece of creative work. But where copyright = all rights reserved, copyleft = all rights released (to use, copy, modify, and sell).

Free software systems can be fast evolving systems because the code is open to everyone, and when someone makes an improvement to a program it is shared with the maintainers. If it's good it will be incorporated into future versions of the program, available to all for free. Some 'flavors' of GNU/Linux are packaged and 'sold', but in reality what is being paid for is the service package and tech support of the packaging company, and source code must be provided with all working versions. Linux itself is available for free to anyone with access to the internet. Other reimplementations of unix for x86 include operating systems like the BSD family, Sun's Solaris, and HP Unix.