Define composition in object-oriented programming.

In object-oriented programming, composition refers to a design principle that reflects a "has-a" relationship between classes. This means that one class contains or is composed of one or more objects from another class, effectively building a complex type from simpler components.

For instance, consider a class called Car. This class may use composition to include several objects, such as Engine, Tires, and Seats. By using composition, the Car class contains these components, which define its structure and functionality. This relationship allows for greater flexibility and reusability; you can create different types of Car classes that may contain different configurations of Engine, Tires, etc.

Composition is fundamental because it promotes code reusability and maintainability, making it easier to change parts of the program without affecting other unrelated pieces. In contrast to inheritance, which establishes an "is-a" relationship and often ties classes together more tightly, composition allows for a more modular and adaptable design.

Understanding this foundational concept is crucial as it underpins many design patterns and principles within object-oriented programming.