expression.ShowWindowsInTaskbar
expression Required. An expression that returns one of the objects in the Applies To list.
Remarks
When set to True, this property simulates the look of a single-document interface (SDI), which makes it easier to navigate among open workbooks. However, if you work with multiple workbooks while other applications are open, you may want to set this property to False to avoid filling your taskbar with unnecessary buttons.
Example
This example specifies that each open workbook won’t have a separate Windows taskbar button.
Application.ShowWindowsInTaskbar = False