Global Address List (GAL)

GAL means Global Address List and it is not quite the same as a company wide address book. The GAL is automatically populated with every mailbox and distribution list and alias on your domain and used most often for auto complete of email addresses when sending email. You can enhance the GAL by entering contact details for users when you create their mailbox accounts, however, the GAL is not a general address book. 

If you require a general address book (shared contacts), create a normal address book in Zimbra and share it to a distribution list which contains all of your users.