Idle time is a period of time during which an employee is not engaged in productive activities. It is usually caused by a work stoppage, or simply because an organization is so overstaffed that there is no need for certain employees.
Businesses try to reduce idle time, since employees are still being paid despite not being engaged in any productive activities. There are a number of ways to do this, such as reducing setup times, cross training employees, and using temporary staff who can be released as soon as there is no work left to do.
However, the drive to reduce idle time does not always work if there is a bottleneck operation involved. In this case, the bottleneck must be deliberately overstaffed in order to ensure that it is operating as close to its theoretical capacity as possible, since the throughput generated by the bottleneck usually exceeds the cost of the extra personnel.