It is a freely available version of the UNIX operating system
It started by Linus Torvalds in 1991.
Programmers from around the world contribute code.
Main portion of Linux: The Linux Kernel.
It can be downloaded from a number of sites (www.linux.org) as well as purchased in packages (called distributions) from companies such as RedHat (www.redhat.com) and Suse (www.suse.com).