Calendar Versioning is a versioning convention based on your project's release calendar, instead of arbitrary numbers.
CalVer suggests version number to be in format of:
YEAR.MONTH.sequence. For example,
20.1 indicates a release in 2020 January, while
20.5.2 indicates a release that occurred in 2020 May, while the
2 indicates this is the third release of the month.
You can see it looks similar to semantic versioning and has the benefit that a later release qualifies as bigger than an earlier one within the semantic versioning world (which mandates that a version number must grow monotonically). This makes it easy to use in all places where semantic versioning can be used.
The idea here is that if the only maintained version is the latest, then we might as well use the version number to indicate the release date to signify just how old of a version you’re using. You also have the added benefit that you can make calendar-based promises. For example, Ubuntu offers five years of support, therefore given version
20.04 you can quickly determine that it will be supported up to April 2025.
Check the Deciding what version system to use for your programs article section.