Epoch

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

In geology, the recent (to the geologist) past is divided into a series of epochs of a few million years each. See Geologic time scale.

In common usage, the term is often used to apply to a period of time when significant related events took place.

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 astronomy, an epoch is a moment in time for which celestial coordinates are specified. The position at other times can be computed by taking into account precession and [proper motion]?.