Social Loafing
 

When people work in groups to perform a task, individual group members may feel less motivated to contribute, since no person is held directly responsible for completing the task. The result is that people may not work as hard, or accomplish as much, as they would if they were working alone and their individual output were being measured. This decrease in personal effort, especially on a simple group task, is known as social loafing. While it is not a deliberate behavior, the consequence of social loafing is less personal efficiency when working in groups than when working on one's own.