What do "n" and "i" mean in swift?

I'm teaching myself Swift and am sometimes able to grasp larger concepts while being unclear on details or why they work.

I figured out how to take an array and use a for loop to cycle through every third element and print them in reverse order.

Is "n" is the element's placement in the array? What exactly is "i"?

let numberArray = ["One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine", "Ten"]


func everyOther() {
    for (n, i) in numberArray.enumerated().reversed() {
         
        if (n+1).isMultiple(of: 3) {
            print(i)
        } //if
    }// for
}// func

everyOther()

Thank you