| pretty sure he means an auxillary input for like Ipod or similar devices so that you can listen to them using your cars audio system. BMW sells on auxillary input for later model cars with the new generation radio. this radio can be identified by the electrical pins being flat. Earlier radios had round pins. On your 2003 car it will prbably have the earlier generation round pin radio. Some people have updated their radios in order to be able to install the aux input which is fairly cheap in price. It may be cheaper to do something aftermarket. If you have an actual IPOD then you may want to look in to the DICE.
Best Regards, | 
