Midnight

Midnight is conventionally 12:00 a.m., the boundary between calendar days and the start of a new date. In ordinary speech, it also means the middle of the night.

12-hour clock: A timekeeping system that divides the day into two 12-hour periods, labeled a.m. and p.m. Its convention assigns midnight the label 12:00 a.m.
Time zone: A region that observes a shared standard time, usually defined by an offset from Coordinated Universal Time. The same instant is midnight in one zone and another hour elsewhere.
Solar midnight: The moment the Sun reaches its lowest apparent position below the horizon at a location. It is an astronomical event, not necessarily 12:00 a.m. on a clock.
Unix time: A system that represents time as seconds elapsed since a defined epoch, commonly 1970-01-01 00:00:00 UTC. Its epoch is specified at midnight UTC, anchoring timestamps to a date boundary.
24-hour clock: A timekeeping system that numbers hours from 00 through 23 within each day. It writes midnight as 00:00, avoiding the 12 a.m. ambiguity.
Coordinated Universal Time: The primary global time standard used to coordinate clocks and civil timekeeping. Local midnight is determined by applying a time-zone offset to this standard.
Solar noon: The moment the Sun reaches its highest apparent position in the sky at a location. It is the daytime counterpart to solar midnight, not always exactly 12:00 p.m.
Cron: A Unix-like job scheduler that runs commands at times specified by schedule rules. A daily job set for 00:00 runs at local midnight under its configured time zone.
Civil time: The time standard used by a society for clocks, schedules, and legal purposes. Midnight on clocks follows locally adopted civil-time rules.
Daylight saving time: A seasonal clock adjustment that advances civil time relative to standard time. A clock change scheduled near midnight can make that local hour unusual.

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