downtime

n. period when a worker is not producing work; period when a computer or machine is not operating due to a breakdown or other reason (Computers, Machinery)

Downtime refers to a period of time or a percentage of a timespan that a machine or system (usually a computer server) is offline or not functioning, usually as a result of either system failure (such as a crash) or routine maintenance. The opposite is uptime.Maintenance downtimes have to be carefully scheduled in industries that rely on nearly 24-hour service, such as e-commerce, medical informatics, news reporting, and persistent online games. In many cases, system-wide downtimes can be averted using rolling upgrades.Downtimes caused by system failures can have serious economic impact. To minimize these effects network monitoring can be used.
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Noun
1. a period of time when something (as a machine or factory) is not operating (especially as a result of malfunctions)
(antonym) uptime
(hypernym) time period, period of time, period

The interval during which a functional unit is inoperable. (188 )

time that a piece of equipment is not available to production, generally due to the equipment being broken or undergoing preventive maintenance.