Encapsulation is a core principle of object-oriented programming(OOP) that involves bundling a class's data (variables) and the methods (functions) that operate on that data into a single unit, or "object". This approach hides the internal details and complexity of the object, providing secure access to its data only through its public methods, a concept known as data hiding. It improves code security, maintainability, and flexibility by allowing developers to change the internal implementation without affecting the external behavior.