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PING Ivy is young and beautiful. I am not so young, and not so beautiful
-- I've been using ping a lot long than she.
Ivy is essentially correct, though ping is really about checking whether you have connections between computers and / or servers on a network.
That network can be a local area network or the Internet.
So, the primary idea is that if you ping an address or a server, you know you have a route or a connection to reach that server or computer -- you know it is online and functioning.
EDIT: I fixed the link. My apologies.