In the version number, e.g:
Moodle 2.8.6+ (Build: 20150625)
What's the + for? Does it just mean there are newer versions available?
It means that it is a weekly release after Moodle 2.8.6, rather than the first official release of Moodle 2.8.6.
Full releases (e.g. 2.8.5, 2.8.6, 2.9.1, etc.) are packaged for download from Moodle.org and announced in the forums (they are monthly, I think).
If you download from git in between a full release, you get a '+' at the end, to signify there are extra changes not included in the full release.
New versions come every 2 months, as stated here :
https://docs.moodle.org/dev/Releases#General_release_calendar
Séverin