In Windows 7, on the extreme right side of the taskbar, you will see a vertical rectangular portion.
Desktop Preview in Windows 7
Moving your cursor to this area will make the open windows transparent and let you preview your desktop. Clicking on it will show the desktop. This is called as the Desktop Preview feature in Windows 7.
But if you don’t like this feature or hardly ever use it, you can always disable it.
Disable the Windows Preview feature
To disable the Windows Preview feature in Windows 7, right-click on the taskbar and click open Properties.
Under the Taskbar tab, you will see a checkbox to Use Desktop Preview. Un-checking it will disable this feature. Click Apply > OK.
Incidentally, right-clicking on the Desktop Preview button will also present you with this option.
Windows 7 offers many new features. It will offer improved navigation, a new taskbar, and a streamlined UI so that common tasks done in Windows are done easier and more quickly. You will be able to share data with all your PCs and devices in your home network or at work.
In Windows 10, you can only disable Aero Peek via Settings > Personalization > Taskbar > Toggle off Use Peek.