epoch

1. (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.Examples: "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."; "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."

2. (geology) A geochronologic unit of hundreds of thousands to millions of years; a subdivision of a period, and subdivided into ages (or sometimes subepochs).Examples: "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."; "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."

3. (machine learning) One complete presentation of the training data set to an iterative machine learning algorithm.Examples: "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."Synonyms: generation