The United States uses a number coding system called the North American Industry Classification System (NAICS) to represent the types of businesses operating in the economy. NAICS can be searched here.
Global Industry Classification Standard (GICS) is a system designed for the needs of the investment community. It uses revenues as a key measure of a company's business activity. It is used in Standard & Poor's products. Read more about it at the MSCI.com site.
So you've found your NAICS code? Great. Here's where to go to use it.
Information producers link the industry codes to their publications, such as reports, articles, and financial data. These databases have the option to search by industry code, as well as keyword, industry terms, company names and subject headings.
Researching the cable industry: Start with a leading company, such as Comcast Corp. Their primary industry is NAICS Code 515210 for Cable and Other Subscription Programming. The first two digits of the code give the sector of the economy. NAICS 51 is the information industry. The first three digits represent a sub-sector of the industry, such as Broadcasting (except Internet) which is NAICS 515.