Object-oriented programming (OOP) is a programming paradigm that organizes code around objects, which are instances of classes. OOP provides a way to structure programs by encapsulating data and behavior into objects, allowing for modularity, reusability, and easier maintenance. Key concepts in OOP include inheritance, where classes can inherit properties and methods from other classes, polymorphism, which allows objects of different types to be treated interchangeably, and abstraction, which hides the internal details of an object, focusing on its essential characteristics. By using OOP, developers can create more robust and flexible software systems.