What is the whole static variable about? This is code to figure that out and ask for help

Static?

public class HelloWorld {
private static final double PI = 3.14;
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		
		System.out.println("Hello World!");
		System.out.println(PI);
		
		for (int PI = 0; PI < 5; PI++)
		{
			System.out.println(PI);
		}
		
		System.out.println(PI);
		int PI = 2;
		System.out.println(PI);
	}

}

/* OUTPUT

0
1
2
3
4
3.14
2

*/