This symbol represents a Database VIEW. To make a view to a linked database use the /LINKED command.
Database views access database information without making the view visible on the website. It is not always desirable to make all database information accessible on a live site.
Clicking the + will allow additional linked databases (and can access multiple different databases).
Tabbed sections (eg. Gallery, List, Table) from the original database can be duplicated but tabbed sections created in database Views will NOT appear on the original database.