Word
Outage
An outage is a stretch of time when the live app is not working for the people trying to use it.
Also called: down, downtime, an incident
Not slow, not missing a feature. Not working.
The word earns its place because it separates the two bad things that look identical from your desk. A change that failed on its way out usually leaves the previous version running happily, and that is not an outage. The app falling over at its own address is.
So the first question in a bad hour is never what went wrong. It is whether anybody outside this room can tell. Different answers, very different afternoons.