A carrier is a business or person that hauls cargo for hire. In the trucking industry, carriers run the tractors and trailers, employ the drivers, and hold the legal operating authority issued by the government. They range from massive fleets with thousands of trucks to independent owner-operators running a single vehicle. Shippers hire them directly or through brokers to move freight.
Carriers are heavily regulated by the FMCSA. They must carry liability insurance, keep safety records, perform truck inspections, and ensure their drivers follow hours-of-service laws. The carrier's safety record is tracked under their US DOT number. A poor safety rating can cause the agency to shut the carrier down or make insurance premiums too expensive to stay in business.