Source : Free On-Line Dictionary of Computing

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)