[iOS] UIApplication object

When you access a UIApplication obeject;

...[UIApplication sharedApplication]...

http://developer.apple.com/library/ios/#documentation/UIKit/Reference/UIApplication_Class/Reference/Reference.html

Every application must have exactly one instance of UIApplication (or a subclass of UIApplication). When an application is launched, the UIApplicationMain function is called; among its other tasks, this function creates a singleton UIApplication object. Thereafter you can access this object by invoking the sharedApplication class method.