The Address book is a collection of address lists such as Contacts, the Global Address List, and the Outlook Address book.
The Outlook Address Book contains the contacts in your Contacts folder and is created automatically. you can also access the Outlook Address Book offline.
Note: The Global Address List only shows when you are using an exchange server or hosted exchange account.
When you are using hosted exchange, the Global Address List contains the names and e-mail addresses of everyone in your organization that has an exchange mailbox. The hosted Exchange administrator can log in to SiteControl, access Exchange admin, and edit individual mailbox information, which ends up appearing in the Global Address List.
The Global Address list is one method of using the power that hosted exchange provides of sharing contacts.