Industries are classified in a number of ways. The most common at this point is NAICS, via the Census, but the SIC, which the NAICS was created to supercede, is still in use, so it's good to know both.
2-6 digit code. NAICS was developed by the U.S., Canada and Mexico in 1997 and is "used by Federal statistical agencies in classifying business establishments for the purpose of collecting, analyzing, and publishing statistical data related to the U.S. business economy." Manual and search are on U.S. Census website.
4-digit code, still used in some government agencies. The U.S. Department of Labor's Occupational Safety & Health Administration (OSHA) maintains the 1987 SIC manual so you can do a keyword search to find the relevant code.
The "Search by Content Type" button on the upper right leads to the menu of everything included in Lexis-Nexis Academic. Go to the Company Dossier for Industry Reports. Search for industries by keyword or SIC code.
Statista culls its data from a number of market research companies, government filings, demographic research, trade groups, and others both domestic and international, and analyzes that data. Some is available without registration but download requires at least a basic account, while a fair amount is behind a paywall.
Industry information from globalEDGE, a thorough resource about international business from the International Business Center at Michigan State University. Reports include background, data sources, regulatory agencies, major players, trade statistics, and more.
An oft-conducted survey of American consumers to determine their satisfaction with goods and services of both domestic and international companies with a major presence in the US. Data is released regularly and includes benchmarks and reports for 43 industries.
"The Economic Census is the U.S. Government's official five-year measure of American business and the economy. It is conducted by the U.S. Census Bureau, and response is required by law." Last done in 2012, next to be done in 2017. Industry Snapshots display Census data and per capita ratios for industries, searchable by NAICS code or title.
Statistics about American businesses that reflect "the number of firms, number of establishments, employment, and annual payroll for most U.S. business establishments," analyzed by geographical area, industry, and business size. Based on the current Census data, conducted in years ending in -2 and -7.