Well, that's true. But I don't see what it has to do with pinging.
The word "ping" comes from an internet protocol (ICMP) used to check to see if another machine is at the destination address. One machine will send out an ICMP echo request to the target address, and if there is a device at that address that can use ICMP (and most do), it will send back an ICMP echo reply. The entire process of sending out the request and receiving the reply is known as a "ping".
In forum terms, the "ping" means that a request for your attention to a particular thread or post is being sent to you. To "ping" someone, simply reply to the thread/post you would like them to look at, and put their name in the "To:" field.
ROTFLMAO!!!