Source : Free On-Line Dictionary of Computing

point of presence
     
        (PoP) A site where there exists a collection of
        telecommunications equipment, usually {modem}s, digital leased
        lines and {multi-protocol router}s.  An {Internet access
        provider} may operate several PoPs distributed throughout
        their area of operation to increase the chance that their
        subscribers will be able to reach one with a local telephone
        call.  The alternative is for them to use {virtual PoP}s
        (virtual points of presence) via some third party.
     
        (1994-12-13)