A higher-order function is a function that can take other functions as arguments or return them as results. This concept is common in programming languages like JavaScript, Python, and Haskell. Higher-order functions allow for more abstract and flexible code, enabling developers to create functions that can operate on other functions, enhancing reusability and modularity. Examples of higher-order functions include map, filter, and reduce. The map function applies a given function to each item in a list, while filter selects items based on a condition defined by another function. These capabilities make higher-order functions powerful tools in functional programming.