Functional application is the act of applying arguments to a function In programming this is usually distinct from simply calling a function.

In a Lisp usually this means taking an actual list of arguments and calling a function with it:

(apply 'car '((1 2 3)))

1

Compare that with:

(car '(1 2 3))

1

In the first instance, the outer list is supplying the list of arguments to car.

In Lisp functional application is the cornerstone of a Lisp interpreter, where often in the source code a function's arguments are quite literally applied to it.

Or, consider the following in JavaScript

const add = (x, y, z) => x + y + z;
console.log(add.apply(null, [1, 2, 3]));

: 6