Closure (computer programming)
Values may be numbers or some other type of data, such as letters, or data structures made up of simpler parts. In the rules of a programming language, the first-class values are values that can be given to functions, returned by functions, and bound to a variable name. Functions that take or return other functions are called higher-order functions. Most languages that have functions as first-class values also have higher-order functions and closures.