It is also popularly used to denote the passing of shorter periods, such as the "[Big Band]?" era, or the death of Frank Sinatra being the end of an era.
ERA is also an acronym for Equal Rights Amendment -- an amendment to the United States Constitution that would have guaranteed full equal rights for women in the United States. The ERA narrowly missed adoption in 1982 when it fell 3 states short of adoption. See http://www.equalrightsamendment.org/era.htm.