Time

UTC

UTC = Coordinated Universal Time, formerly known as Greenwich Mean Time (GMT).

Leap Second

a one-second adjustment that is occasionally applied to Coordinated Universal Time (UTC), to accommodate the difference between precise time (as measured by atomic clocks) and imprecise observed solar time (known as UT1 and which varies due to irregularities and long-term slowdown in the Earth’s rotation).

epoch

The point where the time starts. For Unix, the epoch is January 1, 1970, 00:00:00 (UTC).

Unix Time

Also known as Epoch time, POSIX time, seconds since the Epoch, or UNIX Epoch time.

The term refers to the total number of elapsed seconds since the epoch, typically excluding leap seconds. Leap seconds are excluded from this total on all POSIX-compliant platforms.