Network Information Service Plus (NIS+) is a directory service protocol used for managing network resources in a distributed environment. It allows administrators to store and retrieve information about users, hosts, and services across multiple systems, making it easier to manage large networks. NIS+ enhances the original Network Information Service (NIS) by providing improved security features and a hierarchical namespace. This allows for better organization and access control of network information, ensuring that only authorized users can access sensitive data. NIS+ is commonly used in Unix and Linux environments.