Era

An era is a broad span of time characterized by distinctive features, events, or developments. The term is used in history, archaeology, geology, and calendar systems to organize or describe periods that share a common identity.

In historical writing, eras group events by cultural, political, or social change. Examples include the Victorian Era in Britain (1837–1901) or the Meiji Era in Japan (1868–1912). In archaeology and art history, eras may be defined by technological or stylistic changes, such as the Bronze Age or the Renaissance (where widely used as a term describing a period of revival and transformation).

Geology and paleontology treat era as a formal unit of the geologic time scale, larger than a period and smaller than an eon. The Phanerozoic Eon contains three eras: Paleozoic, Mesozoic, and Cenozoic, representing major chapters in animal life and crustal history. These eras are part of a hierarchical system that includes eons, eras, periods, and epochs.

In calendrical usage, "era" often marks a starting point for dating. The most common is the Common Era (CE) and Before Common Era (BCE), equivalents of AD and BC. The term can also refer more loosely to a notable period in technology, culture, or science, such as the digital era or the space era.

Etymology and usage vary by language, but the concept remains: eras denote spans of time defined by notable changes rather than fixed calendar subdivisions.