idle time

(computer science) The time during which a piece of hardware in good operating condition is unused.
(industrial engineering) A period of time during a regular work cycle when a worker is not active because of waiting for materials or instruction. Also known as waiting time.

The duration of time a device is in an idle state, which means that it is operational, but not being used.

Unproductive time spent by employees due to factors beyond their control.

Investopedia Says:
A power outage is an example.

Cost of direct labor for employees unable to perform their assigned tasks because of machine breakdowns, shortage of materials, power failure, sloppy production scheduling, and the like. The cost of idle time is treated as part of factory overhead-that is, as part of indirect manufacturing costs that should be spread over all the production of a period.