An industry is defined as a group of firms that produce similar or identical products or services within a particular sector of the economy. This collective output represents the industry’s contribution to the market. When multiple firms come together in an industry, they may compete against each other while also contributing to the overall supply of a product or service that addresses a certain demand.
In this context, the option indicating a group of firms producing the entire output of a particular job captures the essence of what an industry is — it encompasses all businesses involved in bringing a particular good or service to market, highlighting their interrelationship and collective impact on supply and market dynamics.
This understanding of an industry aligns with economic principles which categorize firms based on their outputs and market behavior rather than by the uniqueness of individual firms or their unrelated business activities. Other options, while mentioning components related to business, do not accurately reflect the cohesive definition of an industry, which is essential for economic analysis.