Ubuntu, the popular Linux distribution, has been on a steady six-month release schedule for eight years. Every four versions, that is, once every two years, one is marked as Long Term Support (LTS). While typical (non-LTS) releases are supported for around 9 months, LTS versions are provided with five years of updates. Of course, each version, LTS or not, is free. The choice to stay on a specific branch is something else entirely.
For most home users, it will probably make sense to pick up the latest version available on your update manager. Of course, each new release will change things and that can be a problem for some users. That said, given that releases come in six-month intervals, it does make sense to keep up with the changes as they happen, rather than fall behind and have a real shock in five years. Enterprise customers, on the other hand, would love to adopt an operating system which never changes, outside of security updates. Windows XP is a recent example of where enterprise customers will actually pay to not upgrade. These customers will benefit most from LTS.
First and foremost, Canonical, the company behind Ubuntu, wants to catch the wave of PC users who are looking to upgrade from Windows XP and Windows 7. It is free, it has a web browser and an office suite, it is stable and secure, and they suggest that it will be easy to deploy and manage for governments and other institutions.
The interface is Unity7, although users will have the option to try Unity8. The latter version is Canonical's attempt to cover all form factors: phones, tablets, TVs, and desktops.
They probably could have chosen a different number, if only for the jokes.
Ubuntu 14.04 LTS is available now at their website. It is free. If you want it, go get it unless you already have it.