Epoch

n. period, era, age; important event

Depending on context, epoch can refer to:Period of timea distinctive historical period or eraa unit of the geologic time scale, less than a period and greater than an agea phase in the development of the universe with distinctive properties
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Noun
1. a period marked by distinctive character or reckoned from a fixed point or event
(synonym) era
(hypernym) time period, period of time, period
(hyponym) Caliphate
2. (astronomy) the precise date that is the point of reference for which information (as coordinates of a celestial body) is referred
(synonym) date of reference
(hypernym) date
(classification) astronomy, uranology
3. a unit of geological time
(hypernym) geological time, geologic time
(hyponym) Holocene, Holocene epoch, Recent epoch
(part-holonym) period, geological period

(n.)
The date at which a planet or comet has a longitude or position.
  

(n.)
An arbitrary fixed date, for which the elements used in computing the place of a planet, or other heavenly body, at any other date, are given; as, the epoch of Mars; lunar elements for the epoch March 1st, 1860.
  

(n.)
A period of time, longer or shorter, remarkable for events of great subsequent influence; a memorable period; as, the epoch of maritime discovery, or of the Reformation.
  

(n.)
A fixed point of time, established in history by the occurrence of some grand or remarkable event; a point of time marked by an event of great subsequent influence; as, the epoch of the creation; the birth of Christ was the epoch which gave rise to the Christian era.
  

(n.)
A division of time characterized by the prevalence of similar conditions of the earth; commonly a minor division or part of a period.
  

1. [Unix: probably from astronomical timekeeping] The time and date corresponding to 0 in an operating system's clock and timestamp values. Under most Unix versions the epoch is 00:00:00 GMT, January 1, 1970; under VMS, it's 00:00:00 of November 17, 1858 (base date of the US Naval Observatory's ephemerides); on a Macintosh, it's the midnight beginning January 1 1904. 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 6.8 years. The 1-tick-per-second clock of Unix is good only until January 18, 2038, 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]