An industry is a group of competitors who manufacture, produce, and/or sell the same or similar products. Industries can be very narrowly or broadly defined based on who is included as a competitor. 

The U.S. government defines industries by NAICS (North American Industrical Classification System) codes.  An industry being defined at a 2-digit NAICS code level is defined at a broad level. An industry defined at a 6-digit NAICS code level is very narrowly defined.

The more specifically an industry is defined, the more challenging the research will be.

To find a company's competitors, look up the company's NAICS code in Business Source Complete.