Installing and upgrading help

Hello

I think you meant 3.3, I doubt anybody would suggest 2.3 .

Currently supported versions are 3.4 and 3.3. I would recommend to always go with the latest version because it will be in support for the longest time. You can find them on download page

You can find the visual representation of latest versions here: https://docs.moodle.org/dev/Releases#Version_support

Term "stable" used by moodle developers to refer to the versions that are already released. This is how the branches in the git repository are called. We also use the term "master" to refer to the next major version that we currently work on. So, answering your question, technically all released versions of Moodle are "stable".