What is the Ubuntu 16.03, 16.05, 15.11, etc? I was typing Ubuntu 16.04 and accidentally typed 16.03. I saw things like Ubuntu 16.03, 16.05, 16.01 on launchpad. They were milestones relating to the next Ubuntu release. What is this about?
These are monthly snapshot-releases corresponding to the milestones for the next official Ubuntu release. They are the product of the time-based release cycle used by Canonical for Ubuntu since version 13.04.
The major version number stands for the year and the minor version for the month of the release (16.06 for June 2016).
- interim releases (also called "standard") every six months: 14.10, 15.04, 15.10;
- major long-term support releases (LTS), every 2 years: 14.04, 16.04;
- point releases which are updates to LTS: 16.04.01.
For a regular user monthly releases might seem similar to "beta version" or "release candidate" used by other companies for their products, although Ubuntu community also releases beta and release-candidate versions of major Ubuntu flavours (see 16.10 proposed schedule).
In short, releases 16.05, 16.06 are not considered updates to 16.04, but steps towards the next official release 16.10 Yakkety Yak (to be published on October 20th, 2016).