a period of time when something (as a machine or factory) is not operating (especially as a result of malfunctions)
"The factory manager announced that we would have to schedule extra shifts because the downtime caused by the conveyor belt malfunction had delayed all shipments."
The amount of time lost due to forces beyond one's control, as with a computer crash.
"After three hours of downtime caused by a server outage, we finally managed to restore the website."