In this article I want to explain how Linux distribution releases work and why that is important. Unlike many other distributions, the Linux Mint developers focus on absolute reliability and stability and consciously choose not to be a leader in all bleeding edge developments. In order to do that, Linux Mint is always based on what is called an LTS, or Long Term Support, release. So in the post I will explain in simple terms the release cycle of a Linux Mint distribution.
The release cycle of Ubuntu
The basis of Linux Mint is Ubuntu. Ubuntu itself offers both a Long Term Support release and a short term but more up-to-date / bleeding edge release. Canonical, the provider of Ubuntu, produces a new version of Ubuntu every six months, in which the latest and best applications are always made available. For this 6-month release you get up to 9 months of support and security updates. In addition, there is also an LTS release. A new LTS version is issued every two years. In older releases, an LTS version had three years of support on Ubuntu Desktop and five years on Ubuntu Server. From Ubuntu 12.04 LTS received both versions of support and updates for five years.
The release cycle of Linux Mint
Probably after reading the above it is a bit clearer for you why the Linux Mint Team uses the LTS version of Ubuntu as a base. LTS receives 5 years of support and security updates compared to the only 9 months of the bleeding edge version. The consequence is that the age of the base for Linux Mint can be up to 2 years, namely the frequency in which a new LTS release for Ubuntu is delivered. Basically, as a Linux Mint user you start to lag behind modern developments, but how bad is that if you have a system in which all teething problems are solved and therefore stands as a house. And that lag is relative, since Linux Mint itself also comes with interim updates (point releases), but always based on the stable LTS releases.
The previous version of Linux Mint is 18.3. This version and also 18.2, 18.1 and 18, are based on Ubuntu Xenial Xerus (16.04 LTS with release date April 21, 2016)) and thus have support until April 2021. These are all still available to download. The most recent version of Linux Mint is 19. This version is based on the LTS release 18.04 Bionic Beaver from Ubuntu, which came out on April 26, 2018. Since the Linux Mint team always needs some extra time after the release of an Ubuntu release latest developments and test work, Linux Mint 19 Tara came out on June 29, 2018. This gives Linux Mint 19, just like Ubuntu 18.04, support until April 26, 2023. At that moment, Linux Mint is equally bleeding edge as Ubuntu 18.04, but if we continue in time Linux Mint will not completely follow updates of Ubuntu, as explained above. Again, this is not automatically a bad thing when you find a stable and reliable system more important than a bleeding edge up to date system.
For more information on the Linux Mint version history see https://en.wikipedia.org/wiki/Linux_Mint_version_history