Debian GNU/Linux is a Linux distribution -- a full operating system and set of utilities and applications based around the Linux kernel. Four major advantages separate Debian from other distros:
  1. It is 100% Free Software. Every package in the Debian main archive is free software, whether under the GPL, BSD License, Artistic License, or another free-software license. This means that all the work done in developing Debian is completely available to the user community. (Another Linux distribution of which this is true is Red Hat Linux.)
  2. It uses a sophisticated package-management system. Most Linux distributions use the rpm package-management system, developed by Red Hat. Debian uses the dpkg system, which is overtly similar but has a few significant differences. A major advantage of dpkg over rpm is that package dependencies are stored in a database separate from all packages, so you can calculate dependencies before you download anything. The dpkg system is designed to work with the APT tools, which make it very easy to keep Debian up to date -- just run apt-get update && apt-get upgrade to bring your whole system to current versions of all packages. (Other distributions that use dpkg and APT include Progeny Debian and the late Corel Linux.)
  3. It is community-developed. Most Linux distributions are developed by a corporation. While there is nothing really wrong with that, it does mean that sometimes decisions can get made on marketing rather than technical bases, which can be unfortunate. In contrast, Debian is developed by its own community of developers, most of whom are volunteers.
  4. It is extensively tested before release. Because the previous point is true, there are essentially no marketing pressures upon the Debian developers forcing them to release a "stable version" before it really is stable. As a result, while the "stable" version of Debian may lag behind other distros, it tends to be rather more stable (and secure too!) Users interested in the latest features can always use the frozen, testing, or unstable development trees, which are often just as stable as other distributions' release versions.

The Debian Web site is http://www.debian.org/. If you are looking for a stable and reliable Linux distribution, especially for server use, Debian might make a good choice.

Update, October 2001: Progeny Debian, mentioned above, no longer exists as a separate distribution. Its features are being rolled into Debian proper, for which Progeny Linux Systems will offer commercial support.