Higher order functions in JavaScript
Functions that operate on other functions, either by taking them as arguments or by returning them, are called higher-order functions. If you have already accepted the fact that functions are regular values, there is nothing particularly remarkable about the fact that such functions exist. The term comes from mathematics, where the distinction between functions and other values is taken more seriously.http://eloquentjavascript.net/05_higher_order.html
Read the article for some clear examples to help you understand the concept.