Ubuntu Linux is a Debian derivative that aims to bring Linux mainstream. Ubuntu is named after the South African philosophy of "humanity towards others," and the community observes a Code of Conduct in an effort to keep the project civil and appealing to novices.
Ubuntu versions are released every six months, following a YEAR.MONTH pattern. For example, the release codenamed Maverick was officially published October 10th 2010 as Ubuntu 10.10. Each release gets the software from the Debian Unstable repository, freezes it and fix and adapt it to Ubuntu philosophy.
Ubuntu Linux is backed by Canonical Ltd., a company founded and funded by south African Mark Shuttleworth, entrepreneur and Debian Developer. The focus of Canonical is to provide support and services to Ubuntu Linux Desktop and Server editions. Canonical employers sometimes develop to Ubuntu and Debian at the same time, that way keeping the contributions flowing back to Debian.
There is a Stack Exchange site dedicated to Ubuntu which is a good place to ask any Ubuntu-related questions.