The Nice Agreement is a multinational treaty overseen by the World Intellectual Property Organization (WIPO) that sets the Nice Classification. It was signed on June 15, 1957, in Nice, and went into effect on April 8, 1961. It was updated on July 14, 1967, in Stockholm, then on May 13, 1977, in Geneva, and modified on September 28, 1979.
It's an international classification system for classifying goods and services in order to register trademarks.