A team is two drivers assigned to the same truck. While one drives, the other rests in the sleeper berth, then they swap — so the truck can keep rolling far more of the day than a single driver legally could.
Because each driver logs their own Hours of Service, a team can cover long distances much faster, which makes them well suited to urgent, long-haul, or hot loads. The trade-off is two drivers to pay, so teams are used where speed justifies the cost.