The North American Industry Classification System (NAICS) is the standard used by Federal statistical agencies in classifying business establishments for the purpose of collecting, analyzing, and publishing statistical data related to the U.S. business economy.
A NAICS code is a 6-digit code. For example:
311 Food Manufacturing
3118 Bakeries and Tortilla Manufacturing
31182 Cookie, Cracker, and Pasta Manufacturing
311821 Cookie and Cracker Manufacturing