Classification codes for trade describe different types of commodities. The larger the number, the more precise the definition.
A two digit code is a broad category while a 5 digit code is a specific product or commodity. US codes are even more specific but can be truncated to fit into the broader international systems..
There are two major systems used to classify imports and exports.
The Standard International Trade Classification (SITC) was developed by the UN and has been in use since 1950.
The code can be browsed online at the UN
The Harmonized System or Harmonized Tariff System was created in 1988 and has been revised more frequently. It is maintained by the World Customs Organization. This code is not freely available.
The US maintains its own codes, which are based on the Harmonized System. These have greater detail than the Harmonized system.