"Usually the desktop and server versions are supported for 18
months. They have bug and security fixes made available for that
time. However, LTS stands for Long Term Support. The desktop verion
is supported for 3 years and the server version for 5 years. So
far, Ubuntu have released two LTS versions, one in 2006 (in June,
it was two months late, so is often referred to as 6.06) and the
current version, 8.04, is also an LTS release."