Rich is spot on, it is indeed an Aux in connector. You can buy a multimedia adaptor off the bay that plugs in and gives you 2 audio phono leads and one video phono lead to that you can connect pretty much anything that has a composite output.
On Rich's photo above, the main quad lock is split into 3 parts. The top 2 smaller pin ones are for telephone and cd changer. The larger lower one is power, can bus and speakers.
