Earlier today, I found a mention of Meta police in a comment
under Why aren't moderation tools given to people with a history
of good moderation?  Allowing those who don't have "skin in the
game" to moderate has its own problems. We already have
complaints about "Meta police"...  Tried to search the term both
here on MSO and on MSE, but found only old mentions of CW
police. What does this term mean? Has it something to do with
users moderating the site without participating in Q&A itself?
"Has it something to do with users moderating the site without
participating in Q&A itself?" <-- that. Whether or not that is
an actual thing though is not all that clear. It seems to be
often used (in various forms) by users who are somehow
dissatisfied with actions taken on their posts or on posts they
like. –  Bart Aug 9 at 13:04 take a look at MSE post pointing
out the phenomenon: 'Another half to this problem is
Lounge<C++>. Not all of them and not all the time, but do a
search of their room for the term "meta police".