Introduction
The address book functions like an address book, phone book and Rolodex,
  allowing you to store or retrieve contact information in a convenient
  manor, and integrated into the other Horde groupware applications.
The address book lets you maintain your own private address book,
  as well as letting you access some public
  internet directories. You may find the address book useful to
  send email to people who have long or complex email addresses (by
  setting nicknames which you can then use as short cuts for their
  addresses) or to make distribution lists for groups of
  addresses.  It can also be used to store other information about
  your contacts.