What is a callback function?

A callback function is defined as a function that is passed as an argument to another function and is intended to be called or executed at a later time, usually after a particular event or action has taken place. This concept is crucial in programming, particularly in asynchronous operations, event handling, or when working with frameworks that utilize callbacks for operations like rendering or data fetching.

For example, when you pass a callback function to an event listener, that callback will be invoked when the event occurs, allowing developers to specify behavior that should happen in response to user interaction or when a certain condition is met. This design promotes flexibility and allows for code reuse, as the callback can be defined in one part of the code and executed at a different time depending on the context in which it's used.

Understanding this concept is essential for working with JavaScript and function-oriented programming, where asynchronous operations and event-driven designs are common.