United States Patent Classification

"The USPC is a system for organizing all U.S. patent documents and many other technical documents into relatively small collections based on common subject matter. Each subject matter division in the USPC includes a major component called a class and a minor component called a subclass. A class generally delineates one technology from another. Subclasses delineate processes, structural features, and functional features of the subject matter encompassed within the scope of a class. Every class has a unique alphanumeric identifier, as do most subclasses.

A class/subclass pair of identifiers uniquely identifies a subclass within a class (for example, the identifier '2/456' represents Class 2, Apparel, subclass 456, Body cover). This unique identifier is called a classification symbol, or simply a classification, or USPC classification, to distinguish it from classifications of other patent classification schemes. A subclass represents the smallest division of subject matter in the USPC under which documents may be collected."