The term 'PERIOD OF YEARS' can be represented by the three-letter word 'ERA'. An ERA is a span of time usually defined by a certain event or set of events. It is often used to refer to a long period of time in history, such as the Stone Age or the Renaissance. It can also refer to a shorter period of time, such as the Cold War or the Industrial Revolution. In either case, an ERA is a distinct period of time that is marked by its own unique characteristics.