NIS is a protocol developed by sun to allow one to differ user authentication to a server. The server software is in the ypserv package, and the client software is in the yp-tools package. ypbind-mt is also available, which is a multi threaded version of the client daemon.
Note: obviously this article is far from finished. hopefully in the future that will change, but in the meantime:
The Linux NIS HOWTO (http://www.tldp.org/HOWTO/NIS-HOWTO/) is very helpful and generally applicable to arch linux.