The Navigator Overflow Panel is only visible in the Office View and holds icons for invisible Navigator groups.  When a group's header is made invisible, the group's icon appears within the view's overflow panel which is displayed at the bottom.

Additionally, the overflow panel displays a sign used to invoke the context menu which allows users to change the number of visible group headers and toggle the visibility of groups.  The menu's structure is shown in the image below. For example, if you do not have either of the Calendar or EARtrak modules, un-checking the icons for those groups will ensure they do not appear on the Navigator bar. Other Program Navigator groups can also be hidden/displayed using this function