NIS stands for Network Information Service, which is a client-server directory service protocol used for distributed systems to maintain consistent data and configuration information. NIS is a mechanism for identifying and locating network objects and resources, and it provides a uniform storage and retrieval system for network information. NIS can manage various types of networks, such as electricity, water supply, gas supply, telecommunications, and street light networks.

In addition, NIS can also be used to maintain and distribute a central directory of user and group information, hostnames, e-mail aliases, and other text-based tables of information in a computer network. NIS stores information not only about machine names and addresses but also about users, the network itself, and network services. NIS clients run processes that request data from maps on the servers, and clients do not make a distinction between master and slave servers since all NIS servers should have the same information.

An NIS domain is a collection of machines that share a common set of NIS maps, and each domain has a domain name, and each machine sharing the common set of maps belongs to that domain. NIS uses a client-server arrangement similar to DNS, and replicated NIS servers provide services to NIS clients.