Directory services are powerful search tools that you can use to find people and businesses around the world. The Address Book supports LDAP (Lightweight Directory Access Protocol) for accessing directory services, and it comes with built-in access to several popular directory services. You can also add additional directory services from your Internet service provider.
Like Internet search tools, directory services use different methods for collecting data, so when you are trying to find people or businesses online, you might try more than one service.