epoch

Etymology

From Medieval Latin epocha, from Ancient Greek ἐποχή (epokhḗ, “a check, cessation, stop, pause, epoch of a star, i.e., the point at which it seems to halt after reaching the highest, and generally the place of a star; hence, a historical epoch”), from ἐπέχω (epékhō, “I hold in, check”), from ἐπι- (epi-, “upon”) + ἔχω (ékhō, “I have, hold”).

noun

1. A particular period of history, or of a person's life, especially one considered noteworthy or remarkable.
   And it occasionally happens that a period in which one had, hitherto, been mainly looking for the coming to birth of new things, suddenly reveals itself as an epoch of fading and decay. 1924, F. Hopman, transl., The Waning of the Middle Ages, translation of Herfsttij der Middeleeuwen by Johan Huizinga
2. A notable event which marks the beginning of such a period.
3. (chronology, astronomy, computing) A specific instant in time, chosen as the point of reference or zero value of a system that involves identifying instants of time.
   Coordinate term: (cartography, engineering) datum
   UNIX epoch; J2000 epoch
   Appendix A gives formulae for the calculation of the orbital elements of the planets at any time referred to the mean ecliptic and equinox of the epoch of noon on 1st January 2000; this is called the J2000 epoch. 2000, Carl D. Murray, Stanley F. Dermott, Solar System Dynamics, Cambridge University Press
   There are two major epoch times associated with most timestamps: 1970-01-01 00:00:00 and 1601-01-01 00:00:00. The first, starting in 1970, is traditionally referred to as POSIX time as it is a common timestamp in UNIX and UNIX-like systems. 2016, Preston Miller, Chapin Bryce, Learning Python for Forensics, Packt Publishing Ltd, page 281
4. (geology) A geochronologic unit of hundreds of thousands to millions of years; a subdivision of a period, and subdivided into ages (or sometimes subepochs).
   Now during the time of the glacial epoch the greatest distance of the sun in winter was 98¼ millions of miles, whereas it is now, in winter, only 91½ millions of miles, the mean distance being taken as 93 million miles. 1881, Alfred Russel Wallace, chapter //dummy.host/index.php?title=s%3Aen%3AIsland+Life%2FVIII VIII, in Island Life
   Phoenix and Lubbock are both caught in severe drought, and it is going to get much worse. We may see many such [dust] storms in the decades ahead, along with species extinctions, radical disturbance of ecosystems, and intensified social conflict over land and water. Welcome to the Anthropocene, the epoch when humans have become a major geological and climatic force. 2012 January, Donald Worster, “A Drier and Hotter Future”, in American Scientist, volume 100, number 1, archived from the original on 2012-01-26, page 70
5. (machine learning) One complete presentation of the training data set to an iterative machine learning algorithm.
   The neural network was trained over 500 epochs.
   For now, let's test and evaluate our GAN by comparing the results from the first epoch with the generated images from the last epoch. 2021, Joe Papa, PyTorch Pocket Reference, O'Reilly Media

verb

1. (sciences, transitive) To divide (data) into segments by time period.
   The continuous data were epoched into segments of 1500 ms (starting 500 ms before visual stimulus onset), time-locked to stimulus onset (0 ms) and sorted according to experimental conditions. July 6, 2015, “Stronger Neural Modulation by Visual Motion Intensity in Autism Spectrum Disorders”, in PLOS ONE, →DOI