A linux distribution created by a committee. Actually more like an army.

http://www.debian.org

Extremely good on the server, the stable distribution is sometimes three years old but currently only six months old. Testing is more up to date, and unstable is (b)leeding edge. Installation is repetitive and assumes knowledge of hardware. Once installed, the infamous APT utilities makes updating a breeze.

Debian requires a fair bit of work so beginners should perhaps start with Ubuntu, which is a full Debian system made easy to install and use.

A GNU/Linux distribution. Debian is a non-profit organisation that produces a "Free" Operating System, in accordance with their own very strict Social Contract guidelines.

For some people, the "freedom from license encumberance" is the reason to use Debian. Note that RMS claims Debian is non-free, because it is possible to install licensed software. Debian claim that the GNU project is non-free, because the documentation licenses are restrictive. You pay your money, and you take your choice!

For other people, the stability of a Debian server is essential. Not only is the Debian "stable" distribution described as "old", it is also described as "bug-free" and "consistent". You always know where the config files are (/etc/<package>), where the startup scripts are (/etc/init.d/<package>), where the documentation is (/usr/share/doc/<package>), because the Debian package maintainers make it so.

Debian "unstable" is continuously updated and is as up-to-date as it's possible to be but frequent upgrades will cause dependency issues a few times a year. The choice between "stable" and "unstable" is a personal one but it seems sensible to use "stable" unless there is a good reason to go "unstable" (especially since "sarge" was released and especially for new users who are less likely to compile their own software and run into library version dependency issues).

Debian also is reasonably unique in that it is very cross-platform. Debian is fully ported to, and supported on :-

AMD64 and SuperH ports are in progress. See http://www.debian.org/ports/ for more information.

The apt-get package management system understands how to obtain and install your software, as well as understanding the dependancies each package has on others. You can ask for individual packages to come from "unstable", and apt-get will tell you if this can be done simply, or whether other packages will need to be upgraded first. This is generally found to be a Very Good Thing Indeed.

Debian is capable of automatically upgrading your applications to fix security holes as they as discovered. Ensure the following line is present in /etc/apt/sources.list:

deb http://security.debian.org/  sarge/updates  main contrib non-free

..then subscribe to the debian-security-announce mailing list and whenever an update is announced for a package you have installed:

$ apt-get update
$ apt-get upgrade

Debian is also capable of upgrading itself from one release to the next. To upgrade from "sarge" to "etch", replace all instances of "sarge" in /etc/apt/sources.list with "etch" then:

$ apt-get update
$ apt-get dist-upgrade

Be wary of using the alias "stable" in /etc/apt/sources.list as you might accidentally upgrade to the newest stable release without intending to.

Backports are available to Debian "sarge" for some packages. Edit your /etc/apt/sources.list as directed by the backports site and then install backported packages with:

$ apt-get install -t sarge-backports xserver-xorg

..or for the brave:

$ apt-get dist-upgrade -t sarge-backports

Learn HOWTO make Debian packages.

The linux.debian.user newsgroup is an excellent place to seek help and advice with Debian. On the web, useful sites include Debian Planet, the Unofficial User Forums, NewbieDoc, and the Debian GNU/Linux Desktop Survival Guide.