What is linux ?

Linux, originally created by Linus Torvald, is an operating system that is freely distributed under the terms of the GNU Public License. It behaves like Unix, but does not come from the same source code base. Linux is available in both source code and binary form.

Linux offers standard Unix features such as multiuser support, multitasking, networking, and POSIX compliance. It supports all the standard Unix utilities (e.g., gcc, Emacs, the X Window System, Ghostscript, bash) and can compile most major Unix packages with little effort. DOS emulation is also available, and an X Window System-based Microsoft Windows compatibility layer is in development.

The complete Linux operating system consists of the Linux core, or kernel, combined with the utilities and applications required for a fully functional operating system. There are several such combinations, called distributions, put out by various companies, and there is no such thing as an official version. For more information on Linux, visit the Unix Systems Support Group (USSG) web site and click the link under Unix Flavors at:
http://www.ussg.iu.edu/

The Linux Documentation Project offers general guides, specific "HOWTO" documents, FAQs, and links to a wealth of other resources at:
http://www.tldp.org