Event - Target vs CurrentTarget

var rectangle = new Sprite();
rectangle.graphics,beginFill(0xff0000 ,1);
rectangle.graphics.drawRect(0, 0, 100,50);
rectangle.graphics.endFill();
// rectangle added to the stage
addchild(rectangle);

var circle = new Sprite();
circle.graphics.beginFill(0xff0000 ,1);
circle.graphics.drawCircle(0, 0,50);
circle.graphics.endFill();
// circle added to the stage
addchild(circle );

// event listener added to the Stage
// Note: event listener added to the container(stage) not to its children(circle, rectangle)
addEventListener(MouseEvent.Click, onClick);

public function onClick(event:MouseEvent):void{
    trace( event.target );
    trace( event.currentTarget );
}