As an Administrator, you can create an unlimited number of distribution lists for your organization. Distribution lists are not "mailing lists" of people outside of your organization; they are meant to help you organize your addresses into groups and send messages to everyone who is a member of that group. For instance, you can create a distribution list called "Sales," and add all of your sales staff to that distribution list. When you send a message to "Sales," it is delivered to every mailbox that is a member of the "Sales" distribution list.
Like mailboxes and contacts, distribution lists appear in your Global Address List (GAL). The following represents an account GAL with mailboxes, contacts, and distribution lists. Note the differences in how each displays in the GAL.