What does ping timeout mean?
My friends (or me) quit with this message:
+++ TheNick Quit (Ping timeout) * TheNick (Mibbit@A8782BEC.C72ED7D3.30C016FE.IP) Quit (Ping timeout)
And other variations on the theme.
The IRC server, in this instance, irc.mibbit.net, routinely 'pings' all of the clients connected to it. This occurs silently to the user. If the client does not respond in a reasonable time, then the IRC server considers this a dead connection and will force the client to disconnect, a ping timeout.
The reason this occurs is out of your hands, and typically out of the hands of the staff. Generally this occurs because of congestion on the internet.
It can, however, be an indication of a server or network problem. For example, if you saw 10 random people all ping out at the same time, that would probably mean that the server network infrastructure is having some issues.
In rare cases, it indicates that the client is too busy handling messages (for example, if a malicious user or spam bot is flooding the users connection) and therefore can not reply in time to the servers request.
Google results for "irc ping timeout"