A repository server is a collection of one or more repositories. When you install the Trillium Control Center client, you create the primary repository server and have the option to create another alternative repository server. After installation, you can create additional repository servers as needed. When you add a repository server you give it a unique name and specify the server's host name and port number.
For more information see the Trillium Installation Guide and the Trillium Repository Administrator's Guide.