The World Customs Organization’s Harmonized System (HS) uses code numbers to define products. A code with a low number of digits defines broad categories of products; additional digits indicate sub-divisions into more detailed definitions. Six-digit codes are the most detailed definitions that are used as standard. Countries can add more digits for their own coding to subdivide the definitions further according to their own needs. Products defined at the most detailed level are “tariff lines”. See Harmonized System (HS).