In SP2013 on-premise, in the CA's Edit User Profile page (/_layouts/15/ProfAdminEdit.aspx). Some properties have a "Database link" icon. What is the meaning?
If you can read the line above the form, It is clearly mentioned that
Use this page to edit this user profile by changing values for the following properties. Properties that are mapped to the external data source will be overwritten the next time user profiles are imported.
The icon indicates that each property of your user profile is mapped with some external data source