NAICS (North American Industry
Classification System) is a 6-digit business activity code system.
This code system is used by business and government to classify business
establishments according to type of economic activity; in the case of the IRS,
it helps the IRS classify the type of business you are operating for purposes
of reviewing your return.
You can use the following link to enter a keyword for the
type of business you are in, and to find the appropriate six-digit NAICS code:
http://www.naics.com/search.htm