Epoch

[ep-uh k or, esp. British, ee-pok] /ˈɛp ək or, esp. British, ˈi pɒk/

noun
1.
a particular period of time marked by distinctive features, events, etc.:
The treaty ushered in an epoch of peace and good will.
2.
the beginning of a distinctive period in the history of anything:
The splitting of the atom marked an epoch in scientific discovery.
3.
a point of time distinguished by a particular event or state of affairs; a memorable date:
His coming of age was an epoch in his life.
4.
Geology. any of several divisions of a geologic period during which a geologic series is formed.
Compare (def 12).
5.
Astronomy.

6.
Physics. the displacement from zero at zero time of a body undergoing simple harmonic motion.
/ˈiːpɒk/
noun
1.
a point in time beginning a new or distinctive period: the invention of nuclear weapons marked an epoch in the history of warfare
2.
a long period of time marked by some predominant or typical characteristic; era
3.
(astronomy) a precise date to which information, such as coordinates, relating to a celestial body is referred
4.
(geology) a unit of geological time within a period during which a series of rocks is formed: the Pleistocene epoch
5.
(physics) the displacement of an oscillating or vibrating body at zero time
n.

1610s, epocha, “point marking the start of a new period in time” (e.g. the founding of Rome, the birth of Christ, the Hegira), from Late Latin epocha, from Greek epokhe “stoppage, fixed point of time,” from epekhein “to pause, take up a position,” from epi “on” (see epi-) + ekhein “to hold” (see scheme (n.)). Transferred sense of “a period of time” is 1620s; geological usage (not a precise measurement) is from 1802.
epoch
(ěp’ək, ē’pŏk’)
The shortest division of geologic time. An epoch is a subdivision of a period.

1. (Probably from astronomical timekeeping) A term used originally in Unix documentation for the time and date corresponding to zero in an operating system’s clock and timestamp values.
Under most Unix versions the epoch is 1970-01-01 00:00:00 GMT; under VMS, it’s 1858-11-17 00:00:00 (the base date of the US Naval Observatory’s ephemerides); on a Macintosh, it’s 1904-01-01 00:00:00.
System time is measured in seconds or ticks past the epoch. Weird problems may ensue when the clock wraps around (see wrap around), which is not necessarily a rare event; on systems counting 10 ticks per second, a signed 32-bit count of ticks is good only for 0.1 * 2**31-1 seconds, or 6.8 years. The one-tick-per-second clock of Unix is good only until 2038-01-18, assuming at least some software continues to consider it signed and that word lengths don’t increase by then. See also wall time.
2. (Epoch) A version of GNU Emacs for the X Window System from NCSA.
[Jargon File]
(2004-06-10)