Post Office Protocol(POP) A {protocol} designed to allow single user computers to retrieve {electronic mail} from a POP {server}. The POP server might be a computer with a permanent {Internet} connection whereas its clients might only connect to it occasionally, e.g. by {modem}. There are (in 1994) three versions: POP, POP2, and {POP3}. Later versions are NOT compatible with earlier ones. [Details?] (1997-03-06)