User Sources/LDAP
From Authentication Tools for Joomla! (JAuthTools)
LDAP is a standard directory access system with interfaces provided from Microsoft Active Directory, Novell eDirectory, openLDAP (used by Fedora and Apple) and Sun. It allows communication with these systems to occur.
The LDAP User Source utilizes this to provide users from LDAP directories by interrogating them for details, such as name and email address, and building a user object that can be later saved.