In object-oriented programming, what does polymorphism allow?

Polymorphism in object-oriented programming refers to the ability of different classes to provide a unique implementation of methods that are defined in a common superclass. This allows objects of different classes to be treated as objects of a common superclass, enabling flexibility and the ability to use a single interface to interact with different underlying forms (or classes).

The power of polymorphism lies in its ability to allow for method overriding, where a subclass can provide a specific implementation of a method that is already defined in its superclass. This means that a single function can operate on different types of objects, which can streamline code and enhance its maintainability. For example, a function that takes a superclass type as an argument can work seamlessly with any subclass instance, thus promoting code reusability.

The other options do not accurately define polymorphism. Direct modification of data fields refers more to encapsulation principles, inheritance deals with acquiring properties and methods from another class, and static type checking pertains to how types are validated at compile time rather than runtime polymorphism.