Ubuntu Server is one of the most popular Linux server distributions as it is heavily based off the Debian Linux distribution, another top Linux distribution. Ubuntu Desktop has made huge efforts to bring Linux to the mainstream on Desktop computers, while Ubuntu Server is known for it's robust architechture, scalability, and ease of use. Created by Canonical LTD., Ubuntu supports many processor architectures and chipsets including x86, OpenStack, ARM, Power 8 and IBM LinuxOne.
Ubuntu LTS Releases
Ubuntu Server releases updates in several formats. Some are short lived in between major versions known as LTS, or Long Term Support. Whenever you are looking to install Ubuntu server, you want to install the LTS version. This means you will have security updates and support for the operating system for a period of 5 years. This gives time to upgrade to newer LTS versions without a lapse in security updates. The current version of Ubuntu Server is 16.04 LTS as of April 21st, 2016.
Ubuntu LTS End of Life
Ubuntu Server and Ubuntu Desktop are supported during the LTS release lifespan with security updates and regular version updates for Ubuntu and packages for that version of Ubuntu. Once the lifespan of a specific Ubuntu LTS version has expired, this is called the EOL, or End of Life. Below are the upcoming EOL dates for Ubuntu Server and some that have already passed.