Accessed in Appearance → Customize → Page Settings → Maintenance mode.
These settings are only available in Rife Pro.
When this feature is active your visitors will be redirected to page that you have selected in Maintenance Mode settings. However this page will be displayed to not logged in visitors without theme header and footer. This means that when you are logged as administrator, then you will see whole page normally, while not logged in users will see only content.
Good example of such situation can be seen here.
More about subject you can read in article on our blog.