BackTrack is a specialized GNU/Linux distribution, based on Ubuntu 10.04, that focuses on providing the latest security tools, primarily for penetration testing and forensics purposes. It is designed to be useful to people with a wide range of skill levels.
BackTrack is not an official Ubuntu derivative, so it is not supported here. Therefore, questions with this tag should also be about Ubuntu in some substantial way. Questions solely about BackTrack should be asked on Unix & Linux.
BackTrack support ended with the introduction of Kali Linux based on Debian.