HS Code stands for Harmonized System Code. It is a coding system that classifies goods being imported and exported internationally. It is used to identify the Customs Tariffs, or Duty Rate, that will be applied to a product when it is received at the destination port of entry. HS Codes can also be used for other things such as making sure banned or hazardous products are not imported.
You can see the HS codes for a product that has been imported in the Shipment History section here:
The main reason you should determine what the HS Code is in the sourcing phase is so that you can work the duty rate into your costs and make sure you can still be profitable. This is an often overlooked step but without knowing what code the product would have you cannot determine its true costs.
Each code corresponds to a percent and that percent is applied to your cost of goods as shown on your commercial invoice. The duty rate owed at the time of importing is then calculated and paid and your goods are released.
HS codes are globally recognized and used by over 205 countries. For more information and some handy tools check out Freightos HS Code Lookup and Finder.
Also, here is the complete US Schedule.