Object-Oriented Programming (OOP) is a programming paradigm based on the concept of "objects," which represent real-world entities or abstractions. Objects encapsulate data, called attributes, and behavior, called methods, into a single unit, promoting modularity and reusability. OOP relies on four key principles: encapsulation, which restricts direct access to an object's data; inheritance, allowing new classes to inherit properties and behavior from existing ones; polymorphism, enabling methods to perform differently based on the context or object; and abstraction, which hides complex implementation details to provide a simplified interface. These principles make OOP effective for building scalable, maintainable, and efficient software systems.