Linux is an open source operating system which runs on multiple platforms, and it's free. It was initially created by a young student Linus Torvalds in 1991. Linux is currently the fastest growing operating system in the world.
An operating system is a collection of programmes on your computer which controls hardware, other programmes, and allows you to interact with the computer. Probably the best known other operating system are variations of Microsoft Windows®.
Is it really free? Well yes and no. If you wanted to spend hours and hours downloading the files from the Internet then its free. However if you want to get hold of an installation CD and manuals these are available for purchase, and can cost between £23 and £140 (compare this to the current cost of Microsoft Windows £140 - £260). However if you know a friend who has already got a copy of the CD then there is nothing to stop you using that since there are few license issues to worry about. Also various magazines frequently include a copy on their cover disks.
Open source means that the software freely available to be modified and enhanced, because of this is not one "standard" version of Linux.. Many organisations have created their own versions of the operating system, packaging them in different ways including different methods of installation, and adding extra programmes. Some of the better known of these distributions are Red Hat, Mandrake, and SUSE.