1. A network program which sends UDP packets to a host, and listens for responses. Used to check if a machine on the Internet is alive and reachable, and measure the Round Trip Time (RTT) between the local and remote host. From Linux Guide @FirstLinux

2. The "ping" command is built into both Windows and UNIX machines as a universal way of testing network response time and performance. The name is really based off the similarity to sonar pings, though many people have create a post hoc acronym "Packet INternet Groper". Example: The ping-of-death attack used IP fragmentation to crash systems. It was so named because the ping program built-in to Windows could be easily told to fragment packets this way. Key point: Even though the ping program is simple, it can be abused. Some versions can be commanded to send packets as fast as possible, which is often done to flood networks. Most versions allow the packet size to be set to a large size, forcing fragmentation. When used with the flood above, it can overload machines since fragmentation reassembly is so slow. Contrast: There is an IRC command called "PING" that is unrelated to the ICMP ping. It is simply the text string "PING", where the target replies with "PONG". From Hacking-Lexicon

3. To check if a server is running. From the sound that a sonar systems makes in movies, you know, when they are searching for a submarine. From Matisse

4. [from the submariners' term for a sonar pulse] 1. n. Slang term for a small network message (ICMP ECHO) sent by a computer to check for the presence and alertness of another. The Unix command ping(8) can be used to do this manually (note that ping(8)'s author denies the widespread folk etymology that the name was ever intended as acronym for `Packet INternet Groper'). Occasionally used as a phone greeting. See ACK, also ENQ. 2. vt. To verify the presence of. 3. vt. To get the attention of. 4. vt. To send a message to all members of a mailing list requesting an ACK (in order to verify that everybody's addresses are reachable). "We haven't heard much of anything from Geoff, but he did respond with an ACK both times I pinged jargon-friends." 5. n. A quantum packet of happiness. People who are very happy tend to exude pings; furthermore, one can intentionally create pings and aim them at a needy party (e.g., a depressed person). This sense of ping may appear as an exclamation; "Ping!" (I'm happy; I am emitting a quantum of happiness; I have been struck by a quantum of happiness). The form "pingfulness", which is used to describe people who exude pings, also occurs. (In the standard abuse of language, "pingfulness" can also be used as an exclamation, in which case it's a much stronger exclamation than just "ping"!). Oppose blargh. The funniest use of `ping' to date 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, and got tired of having to run back to his console after each cabling tweak to see if the ping packets were getting through. So he used the sound-recording feature on the NeXT, then wrote a script that repeatedly invoked ping(8), listened for an echo, and played back the recording on each returned packet. Result? A program that 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. From Jargon Dictionary

5. send ICMP ECHO_REQUEST packets to network hosts From whatis