How to quit an unresponsive application using Force Quit – Mac OS X
To force quit an application, choose Force Quit from the Apple menu (or press Command-Option-Esc), then choose the unresponsive application in the Force Quit window, and click Force Quit.
Optionally, you may be able to Option-right click the application’s icon in the Dock and choose Force Quit from the contextual menu.
Additionally, you can force quit the front-most application in Mac OSÂ XÂ v10.5 or later by pressing Command-Option-Shift-Esc for three seconds.