Packet InterNet Groper
(ping, originally contrived to match submariners' term for the sound of a returned sonar pulse) A program written in 1983 by Mike Muuss (who also wrote TTCP) used to test reachability of destinations by sending them one, or repeated, ICMP echo requests and waiting for replies. Since ping works at the IP level its server-side is often implemented entirely within the operating system kernel and is thus the lowest level test of whether a remote host is alive. Ping will often respond even when higher level, TCP-based services cannot.
Sadly, Mike Muuss was killed in a road accident on 2000-11-20.
The funniest use of "ping" was described in January 1991 by Steve Hayman on the Usenet group comp.sys.next. He was trying to isolate a faulty cable segment on a TCP/IP Ethernet hooked up to a NeXT machine. Using the sound recording feature on the NeXT, he wrote a script that repeatedly invoked ping, listened for an echo, and played back the recording on each returned packet. This caused the machine to repeat, over and over, "Ping ... ping ... ping ..." as long as the network was up. He turned the volume to maximum, ferreted through the building with one ear cocked, and found a faulty tee connector in no time.
Unix manual page: ping(8).