NIS (formerly called Yellow Pages) allows network management of important administrative files (e.g. the password file). For more information refer to the NIS manpage and Introduction to YP/NIS. There is also a book called Managing NFS and NIS by Hal Stern.
To get these functions to work, you have to configure PHP with --with-yp(PHP 3) or --enable-yp(PHP 4).
The constants below are defined by this extension, and will only be available when the extension has either been compiled into PHP or dynamically loaded at runtime.