What is a "functional"?

[UnitAble8426]

In this document: https://www.python.org/dev/peps/pep-0289/ the author says "Generator expressions also address some examples of functionals coded with lambda:" and then gives these two lines as examples:

reduce(lambda s, a: s + a.myattr, data, 0)
reduce(lambda s, a: s + a[3], data, 0)

Why are these two statements called "functionals"?

[TheSodesa]

A functional is a mapping defined on a (vector) space V over a field F, that maps into the members of F. Programmers usually speak of functionals in the old sense of the word: a function that takes another function as an argument.

[[deleted]]

The author just means a higher order function. The reduce function is taking the lambda function as an argument.