A term often coined in technology industry. Used as a measure of time to state how long a computer system was down. For example: “Our firewall had a downtime of 2 minutes” implies the system was down for 2 minutes. Note that downtime says little to nothing about stability or quality since a scheduled downtime might not interfere with the actual ability of users to use the (computer) system. In the firewall example stated earlier it is not clear the downtime was scheduled or not. “Critical downtime” makes the distinction between unimportant and important downtime. Arguably, downtime says more about stability, quality than uptime.
TakeDown.NET -> “Downtime”