The Lightweight Directory Access Protocol (LDAP) is used to access directory services over a network. A directory is a hierarchically organized data store that may contain any kind of information but is commonly used to store personal data such as names, telephone numbers, e-mail addresses, and job functions. Common examples of LDAP are the Active Directory used within Windows domains, and OpenLDAP, used in various situations. You are most likely to encounter LDAP being used in corporate intranet-based web applications, such as an HR application that allows users to view and modify information about employees.
Each LDAP query uses one or more search filters, which determine the directory entries that are returned by the query. Search filters can use various logical operators to represent complex search conditions. The most common search filters you are likely to encounter are as follows: