Every now and then an application will freeze or lock up. When this happens you can no longer work with that application or your documents. Very rarely, you will not be able to access other applications; A big clue that an application has become unresponsive is when you get the spinning beach ball for a long period of time. The "Force Quit" command allows you to kill an unresponsive program, allowing you to quit the application. You can then either restart that application or continue working with other applications.

WARNING
Killing an application with the "Force Quit" command will quit the application without saving. Any unsaved documents will be lost. Use the "Force Quit" command only as a last resort when you cannot access the standard quit.

To force quit an application

Select "Force Quit" from the Apple menu or press Option, Command, Esc (at the same time).

 

You will then get a Force Quit window. Select the application you wish to force quit and click "Force Quit".

 

You will then have to confirm that you want to force quit the selected application.