Kevin is right, but the reason for being labeled as such, here is this definition of ping:
ping [pɪŋ]
n
a short high-pitched resonant sound, as of a bullet striking metal or a sonar echo
Watch any naval battle movies or submarine movies? Before submarine's had all their hi-tech navigation of today, they were able to tell distance, by sending out an echo (a ping) towards an object, which reflects back telling them the distance based upon length in time, similar to what a dolphin does.