A fixed point of time, usually an epoch, from which a series of years is reckoned.
- A period of time as reckoned from a specific date serving as the basis of its chronological system.
- A period of time characterized by particular circumstances, events, or personages: the Colonial era of U.S. history; the Reagan era.
- A point that marks the beginning of such a period of time. See Synonyms at period.
- The longest division of geologic time, made up of one or more periods.