A zone is a way to map multiple Web application configuration settings to a single set of content databases.
For example, you can create a Web application, create a content database, and then configure the database to use Windows authentication.
All of these settings are configured for the Default zone for the Web application. You can then extend the Web application and map it to a new zone. When you do that, you select a zone to map to, such as Intranet, Internet, Custom, or Extranet.
When you configure the second zone, you select an existing or new Internet Information Services (IIS) virtual server and a new load-balanced URL, and determine whether to use NTLM or Kerberos authentication. You can change the authentication provider, for example, to forms authentication, after the new zone is created.