An HS or HTS code stands for Harmonized System or Harmonized Tariff Schedule. Developed by the World Customs Organization (WCO), the codes are used to classify and define internationally traded goods. In most cases, in order to import or export a product internationally, the traded good must be assigned an HTS code that corresponds with the Harmonized Tariff Schedule of the country of import.
The difference between an HS code and HTS code is the number of digits within the code. A code with six digits is a universal standard (HS Code) and a code with 7-10 digits (HTS Code) is often unique after the 6th digit and determined by individual countries of import.
These codes are important because they not only determine the tariff/duty rate of the traded product, but they also keep a record of international trade statistics that are used in nearly 200 countries. For example, the United States Census uses these codes to determine the value, quantities, weights, countries traded with, and more, of every product that the United States imports and exports.
This link lists the entire Harmonized Tariff Schedule for the United States: https://www.datamyne.com/hts/. You can drill into any schedule to see import and export values for any of the HS and HTS codes.
These codes go from 2-digit chapters and narrow down to a specific 10-digit code. Currently there are 99 chapters (132 including subchapters).
Each section of the 10-digit HTS code represents a predefined nomenclature. See a definition of each HTS section in the graphic below. Try clicking into a 10-digit HTS code (Click Here). Notice how the HTS code becomes more defined and segmented as the number of digits increase.