What does the 'override' keyword indicate when used in a subclass?

The 'override' keyword in Kotlin is used in a subclass to signify that the subclass is providing a new implementation of a method that is already defined in its parent class. This is a fundamental feature of object-oriented programming, allowing subclasses to modify or extend the behavior of inherited methods.

When a method in the parent class is marked as open (i.e., it can be overridden), the subclass can use the 'override' keyword to create its own version of that method, tailoring its behavior to fit the needs of the subclass. This allows for polymorphism, where a subclass can implement a method differently than its superclass while still adhering to the same interface.

For example, if a class Animal has a method makeSound(), a subclass Dog can override this method to provide a specific implementation like barking. This enhances code reusability and allows for more dynamic behavior in your applications.

The other choices do not accurately describe the function of the 'override' keyword in the context of subclassing and method implementation. Instead, they imply restrictions or qualities about method accessibility that are not the direct implications of using 'override'.