Unix time

Unix time represents an instant as the number of seconds since 00:00:00 UTC on January 1, 1970, excluding leap seconds.

Unix epoch: The reference instant 00:00:00 UTC on January 1, 1970, used as the origin for Unix timestamps. Unix time measures elapsed seconds from this fixed starting instant.
Timestamp: A value that identifies a date and time, often in a standardized numeric or textual format. Unix time is one widely used numeric form of timestamp.
System clock: A computer’s maintained estimate of the current time, used by operating systems and applications. Unix time is a convention for representing readings obtained from system clocks.
Time zone: A geographic region whose clocks follow the same standard offset and seasonal rules relative to UTC. Unix time identifies an instant independently of the local time zone used to display it.
Coordinated Universal Time: The international time standard that provides the basis for civil timekeeping worldwide. Unix timestamps use UTC to define the epoch and interpret instants.
ISO 8601: An international standard for representing dates and times in textual formats such as 2025-03-08T14:30:00Z. It expresses calendar dates directly rather than counting seconds from an epoch.
Monotonic clock: A clock source that never moves backward and is intended for measuring elapsed durations. Unlike Unix time, it need not correspond to a civil date or UTC instant.
Daylight saving time: A seasonal clock adjustment that shifts local civil time, usually by one hour. Unix timestamps remain epoch-based while displayed local times can shift seasonally.
Leap second: A one-second adjustment occasionally added to UTC to keep it close to Earth’s rotation. Unix time excludes leap seconds, so it does not count every UTC second uniformly.
Network Time Protocol: A protocol for synchronizing computer clocks over packet-switched networks. Systems often convert synchronized clock readings into Unix timestamps.

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