DecimalFormat Class (Question on what the # does)

[s3a]

Here is my code:

import java.text.DecimalFormat;

import java.util.Scanner;

public class decform_checker
{
	public static void main (String [] args)
	{
		Scanner kb = new Scanner(System.in);
		
		double number = kb.nextDouble();
		
		DecimalFormat formatter = new DecimalFormat("#0,000.000%");
		System.out.println(formatter.format(number));
	}
}

I would appreciate it if somebody could explain what the # does in detail because I don't understand what I read on it and I don't find much to read about it either.

Thanks in advance!