Mac OS X,  Mac OS X Server,  Mac Security

Mac OS X: What is Open Directory?

Technically speaking, Open Directory is an LDAP database that can be used to store information about users, contacts, computers, groups (of all of the above) and other devices.  The reason we do not call Open Directory LDAP is that it also has other components.  These include Kerberos for single sign-on, SASL for integration with other services and password server, to keep the passwords you use secure.