What is Linux?

Linux is a free Unix-type operating system originally created by Linus Torvalds with the assistance of developers around the world.

Licensing

Linux is developed under the GNU General Public License: the source code for Linux is freely available to everyone. It's free software!

Technically

Linux is an independent POSIX implementation and includes true multitasking, virtual memory, shared libraries, demand loading, proper memory management, TCP/IP networking, and other features consistent with Unix-like systems.

Politics

Linux is often called GNU/Linux since much of the code and utilities (in particular the C compiler and associated bits and pieces) was written by people associated with the GNU Project (which in turn is associated with the Free Software Foundation).

In Practice

Linux is an easy to install and use operating system, which is more stable than Windows, is truly multi-user and has a choice of user-interfaces including GNOME and KDE.