In technical networks the networking utility ping is used to test connectivity and response time of network partners.
It's work is quite simple: some host sends a message "ping" to one of his neighbors and waits for a message "pong" to come back.
We do similar in our social network. If you get a social ping, you are invited to answer with a short message.
So we can see whether some particular communication channel is working and learn something about response times.
In your answer you can say something about your availability at the moment (for example: "listening, but have no time until XYZ" ).