Source : Free On-Line Dictionary of Computing

Network Information Service
     
         (NIS) {Sun Microsystems}' Yellow Pages
        (yp) {client-server} {protocol} for distributing system
        configuration data such as user and host names between
        computers on a network.
     
        Sun licenses the technology to virtually all other {Unix}
        vendors.
     
        The name "Yellow Pages" is a registered trademark in the
        United Kingdom of British Telecommunications plc for their
        (paper) commercial telephone directory.  Sun changed the name
        of their system to NIS, though all the commands and functions
        still start with "yp", e.g. {ypcat}, {ypmatch}, {ypwhich}.
     
        {Unix manual pages}: yp(3), ypclnt(3), ypcat(1), ypmatch(1).
     
        (1995-04-08)