Network Information Service definition networking, protocol
(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
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).