What the map is doing in this example is taking the current element (x), the index of the current element (i), and the array that .map was called upon (arr) - the x, i, and arr are just variables that you can name whatever you wish but they will always reprsent the element, index, array in that order. Sometimes you only want the array when using a map, but the only way to do that is to include the element and index regardless.

However if you only need the element you can write something as simply as .map((x) => x ** num), ignoring the index and array.

You can read more about it on the MDN here: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/map