Aero Peek (Show Desktop)
The taskbar on Windows 7 has many different options available, one of which is the Aero Peak Icon. This is located in the far right bottom, next to the time and date.
This option is intended for those users who have to frequently refer back to the desktop, but do not have the time to continually shrink and open new tabs. By simply hovering the mouse arrow over this Icon, the current screen will fade away, exposing your Desktop. Moving the mouse away from the Icon will bring back the screen that you were using.
If you click on the aero peek icon it will take you to your desktop. If you click on the icon again it will bring back the windows you have previously.
How to Disable or Enable Aero Peek
Right click on the areo peek icon. A check next to "Peek at desktop" means its enabled. Click this option to toggle it off and on.