What does the " - " connote?

When in THREE-pane view – in the column in between the Sidebar/DB list, and the DB’s Group list – a few icons are visible.

The Flag icon presumably means that the corresponding/adjacent Group has flagged items in them. What is the " - " telling me?

Attached is a screen-grab:


Its telling you that not all the items in the folder have the same status. That is some items are flagged and others not. If all the items in the folder were flagged there would be a flag and not a “-”.