Ubuntu 11.10 (aka Oneiric Ocelot) is the 15th release of the Ubuntu Linux distribution. It was released in October, 2011, and will be supported by Canonical until April 2013. Canonical is the company which supports the development of Ubuntu and related software products.
The previous release of Ubuntu was 11.04, (Natty Narwhal). To see how Oneiric is different from Natty, view the Release Notes.