[identity profile] caranfindel.livejournal.com 2018-02-06 08:16 pm (UTC)(link)
It's a baseball metaphor about sexual activity leading up to intercourse:
https://www.urbandictionary.com/define.php?term=fourth+base

There is actually no "fifth base," at least as far as the non-Rowena part of the world knows. But it does make you wonder what could be out there. :-)

[identity profile] junkerin.livejournal.com 2018-02-07 09:05 am (UTC)(link)
thank you I checked it