# epoch

Pronunciation: US say "EP-uhk" /ˈɛp.ək/; UK say "EE-pok" /ˈiːpɒk/

## Noun

1. A particular period in history or in a person's life, especially one seen as notable or remarkable.
   - Simple: A period of time in history or in someone's life, especially an important or special one.
   - _The printing press opened a new epoch in the spread of ideas across Europe._
   - _She looked back on her years in Paris as the happiest epoch of her life._
2. A unit of geologic time forming part of a period and divided into ages or sometimes subepochs, lasting anywhere from thousands to tens of millions of years.
   - Simple: A unit of Earth's history, part of a larger period, lasting anywhere from thousands to many millions of years.
   - _Mammoths roamed much of the Northern Hemisphere during the Pleistocene epoch._
   - _Geologists divide the Neogene period into two epochs, the Miocene and the Pliocene._
3. A specific instant chosen as the reference point, or zero, of a system for identifying moments in time.
   - Simple: A chosen moment in time that a system uses as its starting point for counting time.
   - _Unix time counts the seconds that have passed since the epoch, midnight UTC on January 1, 1970._
   - _GPS receivers count time in weeks and seconds from the GPS epoch, midnight on January 6, 1980._
4. One complete pass of the whole training data set through an iterative machine learning algorithm.
   - Simple: One full pass in which a computer program that learns goes through all of its training data.
   - _The model's accuracy stopped improving after about twenty epochs, so we halted training._
   - _Each epoch took nearly an hour on a single GPU._

## Other meanings

- (noun) A notable event that marks the beginning of an important new period in history or in a person's life.
- (verb) To split data, such as a continuous recording, into segments by time period.

## Origin

Ancient Greek ἐπι- (epi-, "upon") and ἔχω (ékhō, "I have, hold") formed ἐπέχω (epékhō, "I hold in, check"). From that came ἐποχή (epokhḗ, "a check, stop, pause"), a word also used for the point where a star seems to halt and so for a historical epoch. Medieval Latin took it as epocha, the source of the English word. Epoche is a doublet.

Source: DictionaryAI, https://dictionaryai.com/define/epoch (written from Wiktionary data, CC BY-SA 4.0: https://creativecommons.org/licenses/by-sa/4.0/).