Standard Industrial Classification (SIC) codes are four-digit codes used for classifying business by industry. Although replaced by the more flexible six-digit NAICS coding system, the SIC code is still widely used for industry classification in the private sector. The Occupational Safety & Health Administration (OSHA) website continues to maintain a SIC Manual.
[Sources: https://www.osha.gov/pls/imis/sicsearch.html]
