Microsoft designed the Windows 7 Taskbar to provide users with quick and easy access to those “things” they use most frequently. The default Out-of-The-Box tasks that’re shipped provide the means to launch a new instance of the application, to pin or unpin an application to the taskbar, and to close the application. You can access the Jump List by right clicking on an application icon in the Taskbar. However, you can opt to take more control of the Taskbar experience by customizing the context of the Jump List for your application.
Full Article: Windows Blog