Ubuntu 14.04 (nicknamed "Trusty Tahr") is a version of Ubuntu which was released initially on 17th April 2014, and support for this version will end in April 2019.
Mark Shuttleworth announced on 31 October 2011 that by the time Ubuntu 14.04 was released, Ubuntu would support smartphones, tablets, TVs and smart screens.
Some time later, on 13th October 2013, it was announced that this version would be nicknamed "Trusty Tahr". Some time later on 17th April 2014, the version was finally released to the public, and available for download.
Support for this version will end in April 2019, and as such, it is suggested that those who are still using Trusty Tahr upgrade to a newer and more supported version of Ubuntu.