Windows 8.1 - How to enable the Peek to Preview feature (Aero Peek)
The Peek to Preview feature of Windows 8.1 (also known as Aero Peek in Windows 7) hides all opened windows when you place the mouse cursor over the Show Desktop button ( located at the right corner of the taskbar).
To enable this feature:
Right-click on the Taskbar > Properties.
Tick the "Use Peek to preview the desktop when you move your mouse to the Show Desktop button at the end of the taskbar".