[Yossarian]

It means a dispatch has been authorised and a picking order has been sent to the warehouse, which means they have it in stock and someone needs to physically get your copy off a shelf put it in the postage medium and leave it with the rest of the days outgoing postage. The next update will say dispatched when the courier/postal company has taken it.

They may only update their systems once or twice a day, so don't panic if the status does not change to dispatched right away, the chances are it will already be well on its way to you before they update their system to show dispatched.