What is a "callback function" in programming?

A "callback function" is defined as a function that is passed as an argument to another function, intended to be executed at a later time, often once a certain condition or event has been met. This concept is prevalent in asynchronous programming, where functions are executed after tasks, such as data fetching or event handling, have completed.

Using callback functions allows for more modular and flexible code, enabling developers to specify what should happen after specific actions, like a response from a server or the completion of a time-consuming operation. For example, a function may fetch data from an API and take a callback function that defines how to handle the response once it is received.

This approach enhances the flow of control in programs, particularly in environments that rely on non-blocking operations, such as JavaScript in web browsers. Thus, understanding and utilizing callback functions is crucial for efficient programming practices in many modern programming languages.