User friendly information about network resources
A directory service or name service, maps the names of network resources to their respective network addresses. With the name service type of directory, a user does not have to remember the physical address of a network resource; providing a name locates the resource. Each resource on the network is considered an object on the directory server. Information about a particular resource is stored as attributes of that object. Information within objects can be made secure so that only users with the available permissions are able to access it. More sophisticated directories are designed with namespaces as Subscribers, Services, Devices, Entitlements, Preferences, Content and so on. This design process is highly related to Identity management.
A lookup is an operation that targets a specific, unique entry, such as a domain name. A search is an operation that targets data common to multiple entries, such as the data collected, by an Internet search engine, about a topic.