Cant understand the programme.

public class week {
	enum Days{
		Sunday,
		Monday,
		Tuesday,
		Wednesday,
		Thursday,
		Friday,
		Saturday
	}
	public static void main(String[] args){
		for (Days d : Days.values()){
			weekend(d);
		}
	}
	public static void weekend(Days d){
		if (d.equals(Days.Sunday))
			System.out.println(d + " Is a holiday");
		else
			System.out.println(d + " Is a working day");
	}
}

I came across this example. In that enhanced for loop they use a code " Days d : Days.values()". Here I can't understand what "Days" in "Days d" refers to.