CONTROL + ALT + DELETE

That's perhaps the most famous key-combination in the whole world: Control + Alt +Delete. If you were used to that on PC's, you might wonder if there is an equivalent in the Mac World. Indeed there is: COMMAND (apple) + ALT (option) + ESC. Whenever you invoke this combination a window will appear, giving you the choice of "force-quit" the unresponsive (and the others too!) applications. Note: You can also "Force-quit" applications by holding the mouse/trakpad button on the dock icon of the unresponsive application.