Packet Internet Groper sends a packet of information to a destination to see whether you get an echo reply (providing that the destination is alive -- and no policies or firewalls or access-lists are preventing transmission). It is a simple way of establishing a connection between two computers using the TCP/IP network protocol.
What it is used for is to test connection speed....handy for online gamers to know so that they can play in real time with others....the lower the better.