NIS (Network Information System) is a network naming and administration system for smaller networks that was developed by Sun Microsystems. NIS+ is a later version that provides additional security and other facilities. Using NIS, each host client or server computer in the system has knowledge about the entire system. A user at any host can get access to files or applications on any host in the network with a single user identification and password. NIS is similar to the Internet's domain name system (DNS) but somewhat simpler and designed for a smaller network. It's intended for use on local area networks.
NIS uses the client/server model and the Remote Procedure Call (RPC) interface for communication between hosts. NIS consists of a server, a library of client programs, and some administrative tools. NIS is often used with the Network File System (NFS). NIS is a UNIX-based program.
Although Sun and others offer proprietary versions, most NIS code has been released into the public domain and there are freeware versions available. NIS was originally called Yellow Pages but because someone already had a trademark by that name, it was changed to Network Information System. It is still sometimes referred to by the initials: "YP".
Sun offers NIS+ together with its NFS product as a solution for Windows PC networks as well as for its own workstation networks.