Lodash Library; dropWhile predicate function

In the Lodash Library exercises, "Implement _.dropWhile() ", step 35, bullet 2:
“The supplied predicate function takes three arguments: the current element, the current element index, and the whole array”.

What is this predicate function and where is it kept?
It seems sort of central to the exercise.

https://www.codecademy.com/paths/web-development/tracks/web-dev-js-arrays-loops-objects/modules/pjs-javascript-capstone/projects/lodash

If you are to make a function that adds two numbers, you don’t get to ask “which numbers will I receive?”
Use what you receive, regardless of which it is.
The whole point of having a parameter for it is so that it can be different things.