ICMP is the INTERNET CONTROL MESSAGE PROTOCOL
you can read the RFC for a full explonation.
there are lots of other sites about this like wikipedia:ICMP
ping is a type of ICMP
0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-------------------------------+-------------------------------+ | Type | Code | Checksum | +-------------------------------+-------------------------------+ | Identifier | Sequence Number | +-------------------------------+-------------------------------+ | Data ... +---------------------------------------------
related: TCP