I found this gem in the What is "meta"? How does it work? subpage of Help Center:
Votes on meta do not affect your reputation; your meta reputation is the same as your reputation on Stack Overflow (synchronized hourly), though you earn separate badges. You must have 5 reputation to participate on meta.
The whole section is actually wrong for this very meta site:
According to this post Merging meta reputation to SO reputation That is not correct because meta SO provides a little bit for all Stack Exchange.
It sounds like an old feature but the about page was never updated..