The outer class is like the name indicates this (see line 3):

package P;

class C {
	
	public static void main(String[] args) {
		new C().start();

	}

}

You could put the word public in front if you want to make it visible for everbody even other packages. Therefore you could see on some websites and forums that they say the, so called, modifier is visible for the world.

This is when you add the modifier public to the front:

package P;

public class C {
	
	public static void main(String[] args) {
		new C().start();

	}

}