Ubuntu is the Linux distribution most well suited to the desktop. We recommend people start by booting Ubuntu from a USB thumb drive on an existing computer. We recommend the most recent LTS version of Ubuntu, currently at 14.04 LTS Trusty Tahr. Each release has both a version number and a code name. The last two digits of the year and the month make up the version number. 14.04 was just released in 2014 in April. Cadence is a core value of the community. Every two years the release is called an LTS or Long Term Support version. This is what many companies and those that don’t require the very most recent software versions. Most non-developers can use the LTS versions just fine.
Ubuntu_(operating_system) wikipedia article
A more rapid cadence for developers is the six month releases. Things move pretty quickly in the software world, but often not many features are added or subtracted unless you are a developer. For most users the amount of time spent upgrading is disruptive and unnecessary though you are welcome to join in at any time.
California and wiki