Some useless information from the courier world: Cargo & shipments are different units. Cargo is the unit for containers and huge-pallets, usually measured by weight. Shipments are contained in cargo as smaller units and measured by volume. Pieces are contained in shipments and are also measured by volume. All can be sent by any mode of transportation, though cargo is usually limited to boat, plane, train and truck.
I had to define the cargo and courier distribution market in a former life. Please shoot me.