Debian is a volunteer-driven project to create a free operating system. Debian GNU/Linux is the flagship product, built around the Linux kernel and base GNU utilities, with thousands of additional programs organized in .deb packages in order to be easily installable.

Debian was created in 1993 (formally on August 16th) by Ian Murdock, at the time a student at Purdue University, and it was intended to be developed in an open fashion, carefully and conscientiously, to be be maintained and supported with similar care (quoted from the Debian Manifesto).

The name "Debian" comes from the name of Ian's wife Debra, combined with his own. It is pronounced deb ee n.

Debian is a unique project because it is the first Linux distribution to be successfully developed in a rather laissez faire system of "benevolent dictators" with a social contract. More than a thousand developers from all over the world volunteer their free time to work on Debian packages, all of which are distributed freely according to a set of licensing guidelines, and all of which are packaged according to a set of technical standards.

The Debian Free Software Guidelines are a pretty simple set of rules a software license has to abide by in order to be considered free enough to be packaged as part of the Debian system. They require free redistribution, sources, right to modify etc. These guidelines have been rather successful, even used to form the Open Source Definition.

The Debian Policy is a rather comprehensive set of rules that a package has to abide by in order to be included in the Debian system. Following these standards allows a high level of integration and consistency on Debian systems. Adherence to the Policy allows Debian packages to be upgraded smoothly.

The Debian packaging system is based on dpkg and APT. They handle the installation, upgrades and removal of .deb packages, make sure configuration files aren't overwritten, that the inter-package dependencies are satisfied and that the package database is consistent overall.

Debian is organized with many checks and balances: prospective developers have to pass several tests in order to be accepted into the group: identity verification, agreement on common philosophy, ability to follow established procedures and actual technical skills to contribute. There is a public system of tracking bug reports, where anyone can file a bug or a wish on each package in Debian, which will have to be processed by the Debian maintainers.

The Debian Project members work on several aspects of Debian: packages are grouped into several distributions:

unstable
This is where the current development happens: packages are uploaded by their maintainer, recompiled on all the various computer architectures Debian supports and distributed to Debian mirror servers, from which the users can fetch them within the same day.
testing
When packages have spent a certain amount of time in unstable without any important bugs on them, they are propagated into testing where they their testing is to be finalized, in order to prepare them for release.
stable
This is the production release of Debian -- at one point, when the package set and the installation system for it is finalized, a snapshot of testing is taken and released as stable. This distribution is then frozen for further updates until the next time a testing distribution is released and given a number. Exceptions are made in case bugs related to security are found.

Debian currently supports almost a dozen computer architectures, which means that it can be installed on all these different types of computers and that all the Debian packages (more than 8700 in Debian GNU/Linux 3.0) are available to the users, from mirror servers and CD vendors in over thirty countries around the world.

Debian continues to grow. In the spirit of providing a choice for everything, Debian systems with different kernels are being developed, such as Debian GNU/Hurd or Debian GNU/FreeBSD. Growing has its pains as well: Debian is often criticized for being too slow to release, which is a problem because of the sheer size and complexity of the system.

A collection of Debian-related links follows.

The Debian web site is http://www.debian.org/

The basics:

Debian Frequently Asked/Answered Questions (but note that it's not exactly the newest version):

Closely related:

Related, but not specifically about Debian:

By/for Debian users:

Miscellaneous:

Of course, if you think anything's missing, /msg me and I'll add it. Most of the links above actually point to nodes with writeups.

Note that in the interest of readability, this writeup contains several generalizations, inaccuracies and other blatant lies. :-)

Standard disclaimer: I'm a Debian developer, so I'm biased.