What is the significance of THIS?

[Army]

I need to know the significance of the keyword this. It seems to me like it does nothing, since I get no errors when I run it without this.

package OOP;
class rect{
	int width;
	int height;
	int depth;
	
		void box(int h, int w, int d){
			this.width = w;
			this.height = h;
			this.depth = d;
		}
		void result(){
			System.out.println(height);
			System.out.println(width);
			System.out.println(depth);
			System.out.println(depth * width * height);
		}
}
public class Rectangle {
	public static void main(String [] args){
		rect objRect = new rect();
		objRect.box(24, 10, 5);
		objRect.result();
	}

}

[KevinWorkman]

First result for googling "java this keyword": Using the this Keyword (The Java™ Tutorials > Learning the Java Language > Classes and Objects)