mirror server Sometimes a Web server will receive more traffic than it can handle. When this happens, the server's administrator may add extra servers--containing identical data--to accommodate the flow. These duplicates are called mirror servers. By adding mirror servers and telling users how to access them, an administrator can keep users from receiving error messages or unacceptably slow response times when they try to access a site. Mirror servers also act as backups if the primary site goes down. See also: server