Acceptable Identification of Goods and Services Manual
The Acceptable Identification of Goods and Services Manual is a directory maintained by the United States Patent and Trademark Office (USPTO) outlining the different categories of goods and services recognized by that office with respect to trademark registrations, and setting forth the forty-two international classes into which those goods and services are divided. The USPTO separates goods and services into various classes, which are governed by international treaties.
Source: Wikipedia — Acceptable Identification of Goods and Services Manual (CC BY-SA 4.0)