Menu item references are used to add alternative drill down links in a report.  When you right click on the output field in the report the list of menu items will be presented in a popup menu.  The easiest way to add menu items to a report is to drag-n-drop them from the menu item node in the AOT.  You can also manually create menu item references by entering the information in the property editor.  When clicked on, the corresponding report (output) or form (display) will be invoked with an Args parameter constructed from the drill down field (see Classes/ClassFactory/drilldown for details on ths).