The Force Quit button enables you to terminate an application. This button is useful if you want to terminate an application that does not respond to your commands.
To add a Force Quit button to a panel, right-click on any vacant space on the panel. Choose Add to Panel -> Actions -> Force Quit.
To terminate an application, click on the Force Quit button, then click on a window from the application that you want to terminate. If you do not want to terminate an application after you click on the Force Quit button, press Esc.