Era

An era is a (usually lengthy) period of time with common characteristics. For example: -- the Biblical era, the Roman era, the Elizabethan era, the Victorian era, the Soviet era. Era is also popularly used to denote the passing of shorter periods, such as the Big Band era, Disco era. Something like the death of Frank Sinatra is called the end of an era. (see also: period)

In Geology, era refers to four well defined time spans covering the history of the Earth. From oldest to youngest, these are the Proterozoic, Paleozoic, Mesozoic, and Cenozoic eras.

A calendar era is the date from which years in the calendar are counted.