Design patterns·Functional ideas that went mainstream
you put the function in a variable, passed it to something and returned it from somewhere else, like any other value.
First-class function
Also calledfunctions as values, first class function
A language property: functions can be stored, passed and returned like any other value. It is the feature that collapses several patterns into ordinary code — a strategy becomes a parameter, a command becomes a closure, an observer becomes a list of functions. Saying that in an interview is a stronger answer than reciting the class diagram for any of the three.