Text is about markwting and commerce :
Standard Industrial Classification (SIC) codes are four-digit numerical codes assigned by the U.S. government to business establishments to identify the primary business of the establishment.
The SIC system arrays the economy into 11 divisions, that are divided into 83 2-digit major groups, that are further subdivided into 416 3-digit industry groups, and finally disaggregated into 1,005 4-digit industries.
http://siccode.com/page/what-is-a-sic-code
Each and every company will have a primary SIC code. This number indicates a company's primary line of business. What determines a company's primary SIC code is the code definition that generates the highest revenue for that company at a specific location in the past year.