SO (Shipping Order)
The carrier's booking confirmation that reserves space on a vessel and allows the shipper to collect an empty container for loading.
TL;DR: The SO is the booking confirmation issued after space is reserved on a ship. In China it is commonly called the S/O, and it is needed to release an empty container and deliver cargo to the terminal.
After the forwarder or shipper books with a carrier, the carrier issues the SO with a booking number. It typically lists the vessel and voyage, port of loading, port of discharge, container type and quantity, ETD, and the key cut-off times. With FCL, the trucking company uses the SO to collect the empty container from the depot. With LCL, the SO tells the seller which CFS to deliver to and by when.
The SO is not the same as the bill of lading. The SO confirms a booking before loading. The bill of lading is issued after the cargo is on board and serves as a receipt and transport document.
Under FOB terms, the buyer’s forwarder usually books the space and sends the SO to the seller, who then arranges loading. Under CIF or CFR, the seller books and holds the SO. Either way, the seller needs it in time to plan production, packing and trucking.
Check the SO details carefully, especially the container type and cut-off dates. For heavy cargo like glass mosaic, make sure the booked container can take the expected gross weight. See Cut-off Time and Bill of Lading.