HTS Codes are short for Harmonized Tariff Schedule. These codes are used to describe the class of product that you are shipping internationally. It is imperative that you enter the correct HS Code for each product you're shipping in the commercial invoice. If you are not sure, call your customs broker and ask them which HTS code you should be using for the product being shipped.
If you do not have a broker, you can call the courier fulfilling the shipment on PaidShipping and ask them. Information on HS Codes, click here.