As per Canonical policy, every regular release will be supported for 9 months and long term releases will be supported for 5 years. While LTS releases for other community flavors will be supported for 3 years. During the support period, Ubuntu will release multiple minor releases with bug fixes and updated packages to make installation less pain for new users.
Ubuntu 12.04 Precise Pangolin was released on 26th April of 2012 is retiring on Friday, 28th April by completing it's 5 years of life time. In Ubuntu fridge blog, you can see an announcement regarding the same.
Ubuntu announced its 12.04 (Precise Pangolin) release almost 5 years ago, on April 26, 2012. As with the earlier LTS releases, Ubuntu committed to ongoing security and critical fixes for a period of 5 years. The support period is now nearing its end and Ubuntu 12.04 will reach end of life on Friday, April 28th. At that time, Ubuntu Security Notices will no longer include information or updated packages for Ubuntu 12.04.