Which object-oriented programming principle allows an object to take on many forms?

Polymorphism is an essential principle of object-oriented programming that allows objects to take on multiple forms. It enables a single interface to represent different underlying data types. This concept is pivotal in enhancing flexibility and reusability of code.

In practical terms, polymorphism permits the same function or method to operate on different types of objects. For instance, a function designed to process a shape can accept various shapes such as circles, squares, or triangles and execute the appropriate behavior for each shape without requiring separate, explicitly defined functions for each type. This capability is often implemented through method overriding in subclass instances or interfaces.

The other options serve distinct purposes in object-oriented programming: encapsulation involves bundling data and methods that operate on that data within a single unit or class, ensuring data protection; abstraction focuses on hiding complex implementation details and showing only relevant attributes and behaviors; and inheritance allows a new class to inherit properties and methods from an existing class, facilitating code reuse without introducing multiple forms per se. Polymorphism uniquely encapsulates the idea that a single interface can represent and manipulate different types of objects seamlessly, making it the correct answer.