Downtime 停机时间
The term downtime is used to refer to periods when a system is unavailable.
Downtime or outage duration refers to a period of time that a system fails to provide or perform its primary function. Reliability, availability, recovery, and unavailability are related concepts.
The unavailability is the proportion of a time-span that a system is unavailable or offline.
This is usually a result of the system failing to function because of an unplanned event, or because of routine maintenance (a planned event).