A standard series of four-digit codes created by the U.S. government in 1937 for categorizing business activities. In 1997, the use of SIC codes was replaced in most (but not all) capacities by a six-digit code called the North American Industry Classification System (NAICS).
Investopedia Says:
The codes are used to promote better communication across business sections and between countries. One major government department that still uses SIC codes is the Securities and Exchange Commission (SEC). The SIC codes are listed in a business's electronic data gathering, analysis and retrieval system (EDGAR) filings in order to indicate the industry to which the company belongs.
For example, if you see that a company has a 3721 SIC code on its EDGAR filing, this means that the company belongs to the aircraft industry.
