A comparator function is a programming tool used to determine the order of two elements. It takes two inputs and returns a value that indicates their relative position: a negative number if the first element should come before the second, zero if they are equal, and a positive number if the first should come after the second. This function is essential in sorting algorithms, such as those used in JavaScript or Python. In many programming languages, comparator functions can be customized to sort data based on specific criteria. For example, when sorting a list of objects, a comparator can be defined to sort them by a particular attribute, like age or name. This flexibility allows developers to create tailored sorting mechanisms for various applications.