Unix Time Glossary

The instant of time chosen as the origin of Unix time, defined as 00:00:00 UTC on Thursday, 1 January 1970. Timestamps are measured as the seconds (or milliseconds) elapsed since this moment.

The primary time standard by which the world regulates clocks and time. It is effectively a successor to Greenwich Mean Time (GMT). Unix timestamps are always based on UTC, regardless of the user's local timezone.

An international standard for the representation of dates and times. The most common format is YYYY-MM-DDTHH:mm:ss.sssZ (e.g., 2024-01-01T12:00:00Z). It is the preferred string format for exchanging date information in APIs.

A one-second adjustment that is occasionally applied to Coordinated Universal Time (UTC) to accommodate the difference between precise time (International Atomic Time) and imprecise observed solar time (UT1).

A networking protocol for clock synchronization between computer systems over packet-switched, variable-latency data networks. It ensures that your computer's clock is accurate to within a few milliseconds of UTC.

A computing issue similar to the Year 2000 problem. It will affect systems that store Unix time as a signed 32-bit integer, which will overflow on January 19, 2038, causing dates to wrap around to 1901.

A high-precision time scale based on the combined output of some 400 atomic clocks around the world. Unlike UTC, TAI does not use leap seconds and flows continuously.

A system for describing points in time, defined by the IEEE POSIX standard. It is essentially Unix time but with a specific definition of how to handle leap seconds (usually by ignoring them), which simplifies calculations but introduces small inaccuracies.

A slang term often used to refer to the Year 2038 Problem, where the 32-bit Unix timestamp counter runs out of bits to represent future dates.

The difference in time between a specific time zone and UTC, usually expressed as +HH:mm or -HH:mm. For example, EST is UTC-05:00. Unix timestamps do not contain offset information.

A clock source that is guaranteed to never jump backwards. It is essential for measuring elapsed time (durations) in software, as opposed to 'Wall Clock' time which can change due to NTP syncs.