In programming, a decorator is a design pattern that allows you to add new functionality to an existing object without modifying its structure. It is commonly used in languages like Python to enhance functions or methods by wrapping them with additional behavior. This makes it easier to extend and maintain code. Decorators are often used for tasks such as logging, access control, or modifying input/output. By applying a decorator, you can keep your code clean and organized, as it separates the core functionality from the additional features. This promotes reusability and adheres to the Single Responsibility Principle.