An industry is a group of companies that are related based on their primary business activities. In modern economies, there are dozens of industry classifications, which are typically grouped into larger categories called sectors. Individual companies are generally classified into an industry based on their largest sources of revenue. For example, while an automobile manufacturer might have a financing division that contributes 10% to the firm's overall revenues, the company would be classified in the automaker industry by most classification systems. Hope This Helps!