"$this" is a pseudo variable used within a class to refer to the class itself. Obviously, since the object hasn't been instantiated yet, we can't use it within the class.

say I have an object $foo

$foo=new myclass();

and a property $bar, I can now call that property

$foo->bar

BUT, within the class code, I don't know I'm going to call the object "$foo", so "$this" is used as a generic reference to the object

I'm just getting my head round classes myself, so I hope that helps

Adam