Shell Extensions are in-process COM objects which extend the abilities of
Windows operating system. Most shell extensions are automatically
installed by the operating system, but there are also many other
applications that install additional shell extension components. For
example: If you install WinZip on your computer, you'll see a special
WinZip menu when you right-click on a Zip file. This menu is created by
adding a shell extension to the system.

The ShellExView utility displays the details of shell extensions
installed on your computer, and allows you to easily disable and enable
each shell extension.

ShellExView can be used for solving context-menu problems in Explorer
environment. For more information, read the following article:
Right-click is slow or weird behavior caused by context menu handler