Era

Span of time defined for the purposes of chronology or historiography

An era is a span of time defined for the purposes of chronology or historiography, as in the regnal eras in the history of a given monarchy, a calendar era used for a given calendar, or the geological eras defined for the history of Earth. Comparable terms are epoch, age, period, saeculum, aeon (Greek aion) and yuga (Sanskrit युग).

From Wikipedia, under CC BY-SA. More on occurri.