| Noun | 1. | uptime - a period of time when something (as a machine or factory) is functioning and available for useperiod, period of time, time period - an amount of time; "a time period of 30 years"; "hastened the period of time of his recovery"; "Picasso's blue period" 24/7 - uptime is 24 hours a day 7 days a week downtime - a period of time when something (as a machine or factory) is not operating (especially as a result of malfunctions) | |