The word epoch can mean either an interval of time, or a particular point in time used as a reference point.

• In common usage, the term is often used to apply to a period of time when significant related events took place. (see also: period, era)
• In geology, the recent (to the geologist) past is divided into a series of epochs of a few million years each. See geologic timescale.
• In computing, an epoch is a specific date and time used as the reference for all other times. The Unix epoch is an example.
• In telecommunication, an epoch date is a date in history, chosen as the reference date from which time is measured.
• In astronomy, an epoch is a moment in time for which celestial coordinates or orbital elements are specified. The current standard epoch is J2000.0
  • In the case of celestial coordinates, the position at other times can be computed by taking into account precession and proper motion.
  • In the case of orbital elements, it is necessary to take account of perturbation by other bodies in order to calculate the orbital elements for a different time.
• The epoch of a calendar era is the year, day, or instant from which the later (and earlier) years of a calendar are counted.
• In gaming, the Epoch was a vehicle capable of time travel in the popular (and now somewhat rare) SNES game, Chrono Trigger. When the player first discovers Epoch, it is only capable of time travel to the exact same point in a different era. Later in the game, however, Dalton modifies it with wings, enabling the player to fly around the world map.