Conversation I had with someone online:
Me: Do you know where [mutual friend] is?
Him: I just got on. Would you like me to ping her?
I’ve heard this word before. What’s it mean? What does someone have to have or do in order to ping someone else? What does it require of both people? How does it work? What would I need to, say, ping someone?
And how does it show where someone is on a site?
Where I work, it means to send an instant message.
But my friend and the mutual friend I shared were both already on an Instant messenger, of sorts. The mutual friend wasn’t replying…so I started out by saying (to my friend) that our mutual friend is on (he probably already saw it) but that she wasn’t replying (I offered maybe it was because the chat was on the fritz…as Facebook chat often is).
So he offered to “ping” her for me.
The way he put it…it sounded like it was more than just offering to just do what I had already been doing, which is IM her.
It means to check on someone, usually by remote means.
In the context of IM it can also mean to “nudge” someone, ie, get their attention.
Originally, “ping” was (well, still is) a computer command which can be used to see whether another computer is connected to the network, how long does the signal take to travel between your computer and that other one, and what route does it take.
It’s also a command available in some networked computer games (it may also be “bell”), where you “/ping Idle” and then, if Idle is on, his computer goes “ping!” So we’ve gone from “calling a computer to say ‘are you there?’” to “calling someone to say ‘are you there?’”
In the situation you describe, it simply means the friend offering to do the pinging has access to some way to contact the other friend that you may not. It can range from sending an IM through a different program to a SMS on the phone to tapping the other person on the shoulder and saying “phone for you.” It’s just nerdspeak for “are you there?” and doesn’t care about the path the message travels, just about relying it.
Then he must simply have meant he was just going to try messaging her too (just like I was and just like I was telling him it didn’t seem to be working). None of the other things apply (it’s stuff he doesn’t know–IE Phone numbers, other IM names, etc).
Thank you for the answers. 
In IRC the pinged computer responds with a “pong.”
Nitpickery: Originally, a ping was a sonar signal sent in the hope of receiving a reflected response from a target. The name of the computer command is an analog to that.
In TCP/IP there is a special packet type (ICMP) which is processed very low in the protocols. It simply asks to be replied to. That is the basis of the ping command. As above, clearly the command took its name from a sonar ping. Finding the route the packets take isn’t part of the ping process, but is a rather clever add on. Packets can have a time-to-live count. Every time they are retransmitted from one host/router to another the TTL count is decremented. When it reaches zero the packet is dead. You get your reply from the host that saw the packet die (unless it is the destination, in which case it always replies.) So if you send a set of ICMP packets, all addressed to the same host, but with TTL values from 1 up (typically to a limit of 20) you can see the presence of any intermediate host that is willing to reply to your request. Many routers on the internet now disable ICMP, so you often see holes in the routing information. It is also worth pointing out that routes are not static, nor singular.
Thank you, I always suspected there had to have been something before that.
You: [Sean Connery voice] One ping only.
I can’t say for certain what Idle Thoughts’ friend meant but ping has long since become a completely non-technical non-specific verb meaning to reach out to someone. I can’t imagine the friend was actually talking about the ping command, but I guess it’s possible.
Idle Thoughts, when people use the word ping colloquially they mean it to be a social analogue to the networking and submarine terms. They’ll reach out to someone in expectation of getting a response. Whatever happens next would be dependent on context.