When you give your item to the USPS for delivery, it accepts your item and starts the process of delivery. Transit is a part of the shipment delivery process. When we say that the package is in the transit or in transit to the destination, it means that the package is on the way to the delivery.
The data bus is Bi-directional because the same bus is used for transfer of data between Micro Processor and momory of input / output devices in both the direction.