From Maties Ubuntu
LTS (Long Term Supported) versions of Ubuntu are available for critical production systems, these have five years free security support with expert paid technical support available from Canonical Ltd.
Any version of Ubuntu that is not an LTS release should be considered testing versions not suitable for production use, but to be used to prepare features for the next LTS release.
The latest LTS release is 12.04, the "Precise Pangolin", also see: https://wiki.ubuntu.com/StableReleaseUpdates
Mark Shuttleworth and Canonical Ltd announced the creation of the Ubuntu Foundation and provided an initial funding of USD $10 million. The purpose of the foundation is to ensure the support and development for all future versions of Ubuntu.