Timestamp & Date
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Unix time
Unix time is the number of seconds that have elapsed since 00:00:00 UTC on 1 January 1970, excluding leap seconds. This time is named the Unix epoch, because it is the start of the Unix time. Unix time is not a true representation of UTC, because leap seconds are not independently represented. Instead, every day in Unix time contains exactly 86400 seconds, with leap seconds sharing the same timestamp as the second immediately before or after them.
Coordinated Universal Time (UTC)
Coordinated Universal Time or UTC is the primary time standard by which the world regulates clocks and time. It is within about 1 second of mean solar time (such as UT1) at 0° longitude (at the IERS Reference Meridian as the currently used prime meridian) and is not adjusted for daylight saving time. It is effectively a successor to Greenwich Mean Time (GMT).
The coordination of time and frequency transmissions around the world began on 1 January 1960. UTC was first officially adopted as CCIR Recommendation 374, Standard-Frequency and Time-Signal Emissions, in 1963, but the official abbreviation of UTC and the official English name of Coordinated Universal Time (along with the French equivalent) were not adopted until 1967.
Time zone
A time zone is an area which observes a uniform standard time for legal, commercial and social purposes. Time zones tend to follow the boundaries between countries and their subdivisions instead of strictly following longitude, because it is convenient for areas in frequent communication to keep the same time.