The North American Industry Classification System (NAICS) is the standard 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. Companies are grouped by industries, according to the NAICS code. Reports, news, and financial data is grouped by this code, so it's important to identify a company's primary industry.

Click on this link to go to the Census Page about NAICS https://www.census.gov/eos/www/naics/

What is the Difference Between an Industry and a Sector? (Answer from Investopedia)

The terms industry and sector are often used interchangeably to describe a group of companies that operate in the same segment of the economy or share a similar business type. Although the terms are commonly used interchangeably, they do, in fact, have slightly different meanings. This difference pertains to their scope; a sector refers to a large segment of the economy, while the term industry describes a much more specific group of companies or businesses.

The easiest way to identify which industry a company belongs to to do a company search on Nexis Uni. You can find the primary industry of a company in the company "Snapshot" page.

Specialized databases like Business Source Complete can search articles using this code.

In order to compare companies in the same industries with each other IBIS reports the key industrial ratios and other measures of industry performance.