I think the article just used this phrase to describe something else. (Great article otherwise).
The short version is that when you have multiple processes waiting on listening sockets and a connection arrives, they all get woken up and scheduled to run, but only one will pick up the connection, and the rest have to go back to sleep. These futile wakeups can be a huge waste of CPU, so on systems without accept() scalability fixes, or with more tricky server configurations, the web server puts a lock around accept() to ensure only one process is woken up at a time.
The term (and the fix) dates back to the performance improvement work on Apache 1.3 in the mid-1990s.
> So many options meant plenty of levers to twist around, but the lack of clear documentation meant that we were frequently left guessing the true intention of a given flag.
And then reading your link, they complain >inside the docs< that the docs aren't complete. I have no idea what to believe anymore :D
Strange read.