A higher order function in JavaScript is a function that either takes one or more functions as arguments or returns a function as its result. Functions in JavaScript are treated as first-class citizens, meaning they can be treated as values and assigned to variables, passed as arguments to other functions, or even returned from other functions. Higher order functions are useful for writing more concise and modular code, and they allow developers to abstract over actions, not just values. Some examples of higher order functions in JavaScript include map, filter, reduce, and addEventListener .