Built on the Linux kernel, Debian GNU/Linux is an open-source and free operating system (OS) that is based on a graphical user interface (GUI). It incorporates GNU project tools and capabilities and is packaged with thousands of software applications for easy installation and execution.
Debian GNU/Linux is also known as Debian.
Techopedia explains Debian GNU/Linux
Released in 1993 by the Debian Project, Debian is a Linux distribution that evolved from the Unix OS. It may be used as a desktop, server or embedded OS and supports a number of processor frameworks, including Intel, AMD and ARM.
Default Debian installation packages are bundled with utility/development tools, communications/email software, networking services and other applications designed for desktops and servers.
As of February 2011, the most current version is Debian 6.0, also known as Squeeze.