Object-Oriented Programming and Design (OOP/OOD) is a programming paradigm that structures software around the concept of "objects" rather than functions and logic. An object is a self-contained entity that bundles together data (attributes) and the behaviors (methods) that operate on that data. Through its core principles—encapsulation, which protects and contains an object's data; inheritance, which allows for code reuse by creating class hierarchies; and polymorphism, which enables objects to be treated in a uniform way despite their different underlying types—OOP facilitates the design of complex systems by modeling real-world entities. This approach promotes the creation of modular, flexible, and easily maintainable code, making it a cornerstone of modern software development.