Which of the following best describes encapsulation in OOP?

Encapsulation in Object-Oriented Programming (OOP) refers to the practice of hiding the internal state of an object and requiring that all interactions with that object occur through well-defined methods. This encapsulation protects the integrity of the object's data by preventing outside code from directly accessing or modifying it. Instead, any changes must go through the object's methods, which can enforce rules, validate inputs, and maintain the object's state in a controlled manner.

This concept enhances modularity and maintainability of code because it allows an object’s implementation details to be hidden from the outside world. Users of the object interact with its public interface, and the complexities of the internal workings are kept private. This way, the internal changes don't affect other parts of the program that rely on the object's API, contributing to a more robust code structure.

The other options describe different aspects of programming concepts but do not accurately capture the essence of encapsulation. The first choice pertains to inheritance, which is a different principle in OOP that involves creating new classes based on existing ones. The third choice relates more to function definition in programming in general, not specific to OOP. The fourth option addresses polymorphism, which involves handling different data types but does not pertain to the encapsulation concept.