Ubuntu LTS, which stands for Ubuntu "Long Term Support," is a stable version of the Ubuntu Linux-based operating system that is largely targeted toward enterprise-grade server environments.
Ubuntu LTS updates are supported by Canonical, the developers of Ubuntu, for five years, as opposed to nine months of support for the non-LTS Ubuntu updates. Ubuntu LTS editions are only released every two years, whereas the non-LTS editions are released every six months.
Ubuntu 14.04 "Trusty Tahr," is the most recent Ubuntu LTS release. Trusty Tahr became generally available in April 2014.