IPA: /ˈʌp.taɪm/
KK: /ˈʌpˌtaɪm/
The period when a machine or system is working and ready to be used.
The server had an impressive uptime of 99.9% last year.
Uptime is formed from "up" (meaning in a higher position or state) and "time" (from Old English "tima", meaning a period or duration). The word "uptime" refers to the period during which a system is operational and functioning properly, indicating a state of being up and running during a specific time frame.
Think of a system being in a higher state ('up') during a certain period ('time') — that's what uptime means.