This is a special Windows Key - a key with the Windows Logo on it.  It's located on most keyboards on the bottom row of keys between the "Ctrl" and "Alt" keys.  It can be used in combination with others for shortcut key controls.  Following, is a list of those keystrokes...

+ "E"	Launch 'Windows Explorer'
+ "Break"	Show the 'System Properties' Dialog Box
+ "D"	Minimize All Windows return to desktop
Shift + + "M"	Undo 'Minimize All Windows'
	Open the "Start Menu"
+ R	Show the "Start" / "Run" Dialog Box