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.
Ubuntu 10.04.x is the LTS edition (Lucid Lynx). It has been designated as a Long Term Support (LTS) release, indicating that it has updates for three years for desktop use and five years for server.
There is a Stack Exchange site dedicated to Ubuntu which is a good place to ask any Ubuntu-related questions.