According to the NAICS website: The North American Industry Classification System or NAICS (pronounced "nakes") is the standard used by Federal statistical agencies to classify businesses according to their economic activity and to collect, analyze, and publish statistical data related to the North America economy. By finding the NAICS code for your industry, you can effortlessly search for information on your sector in library databases, as well as online (Google, etc.).
Note: Please keep in mind that there might not be a NAICS code for your business. In this case, use one similar to your business.
Use the NAICS Code to determine which industry (or industries) best reflect or fit your primary lines of business (product or service). Industry codes provide practical ways to search for company and industry reports in many statistics databases.
Each business is classified into a six-digit NAICS code number based on its primary business activity in the industry. NAICS codes are also required by Federal, state, and local governments for administrative, taxes, or contracting purposes. NAICS is a two- through six-digit hierarchical classification system, offering five levels of details.