HTS code
The Harmonized Tariff Schedule code: the numeric classification every product gets for customs. It decides the duty rate and the statistics a shipment reports.
The first six digits are the international Harmonized System, shared by every member country. Each country then extends the code: the United States uses the ten-digit HTSUS published by the USITC. The code on your commercial invoice sets the duty rate, so a wrong code means wrong money.