Historic Span is a term used to describe a period of time in history. It can refer to an ERA, which is a long period of time marked by certain characteristics, or an AGE, which is a shorter period of time with its own unique features. The two terms are often used interchangeably, but they do have distinct meanings. An ERA is typically defined by a major event or series of events, while an AGE is usually defined by a particular style or set of beliefs.