GAL (global address list)

A list that contains all Exchange users, contacts, groups, conferencing resources, and public folders in an organization. This list is retrieved from the global catalog servers in Active Directory and is used by Outlook clients to address messages or find information about recipients within the organization. [Exchange 2003]

A directory that contains entries for every group, user, and contact within an organization's implementation of Exchange Server. [Exchange 2007]

Contains mailboxes, custom recipients, distribution lists, and public folders in an organization. [Exchange 5.5]