What is the port on the top of the xbox 360 controller?

and what is it used for. I wasent able to find any wires for it. What is the port on the top of the xbox 360 controller?
Its where you plug the play'n charge kit into the controller. So that you can charge the rechargeable battery while you're playing.What is the port on the top of the xbox 360 controller?
Its for use with the Xbox 360 Wireless play and charge kit. You basically replace your battery pack with a lithium battery and charge it up through the small socket on the top of the controller.
It is for wiring the controller to the Xbox 360 when your batteries run out of juice.