Source : Free On-Line Dictionary of Computing

Service Access Point
     
         (SAP) The {OSI} term for the component of a
        network address which identifies the individual application on
        a host which is sending or receiving a {packet}.
     
        {TCP/IP}'s equivalent term is "{port}".
     
        Different SAPs distinguish between different services or
        applications on a host, e.g. {electronic mail}, {FTP}, {HTTP}.
     
        (1996-12-23)