What is strong (iOS4 = retain ) in Objective C?

-it says "keep this in the heap until I don't point to it anymore"
-in other words " I'am the owner, you cannot dealloc this before aim fine with that same as retain"
-You use strong only if you need to retain the object.
-By default all instance variables and local variables are strong pointers.
-We generally use strong for UIViewControllers (UI item's parents)
-strong is used with ARC and it basically helps you , by not having to worry about the retain count of an object. ARC automatically releases it for you  when you are done with it.Using the keyword strong means that you own the object.

Example:
@property (strong, nonatomic) ViewController *viewController;
@synthesize viewController;