Sometimes you may need to check whether your fan page application viewer is the administrator of the page or not. You may provide some special information for the administrator of the page. Like you may provide a control panel to control the application so that the administrator can modify or update the application within the same page. So if you want to do something like that then use the following fbml tag in your facebook fan page application:
<fb:visible-to-owner> You're Admin Dude!!!! This information only shows to admin </fb:visible-to-owner>
So the information within <fb:visible-to-owner> will only show to administrator of the page. Other users will not see the information.