Available Ubuntu Releases.
18.04 LTS, 17.10, 16.04 LTS, 14.04 LTS -- The Ubuntu version numbering scheme is based on the date
of the release of the distribution, April 2018, October 2017, April 2016, etc
16.04 LTS -- The LTS means long-term support (5 years).
Release -- Server and Desktop editions. They have similar packages, but different kernels.
The server may have no X-desktop environment installed.
To check what version of Ubuntu is running on your system run command:
Supported architectures -- x86 (32 bit) and x86_64 (64 bit).