The Era name or Nengō (年号) naming system
The Japanese do not use a calendar year system as we do in most part of the world but give a different name at each period of reign of each emperor. This system is still used today for official purpose. But it is quite impossible to remember or calculate the actual calendar year specially before Meiji when the emperor has changed every few years. Therefore, from 1603 up to 1867, the Tokugawa period is very often and commonly refered to Edo period. Then we distinguish roughly early, middle or late Edo which are then followed by Meiji and Taisho periods. The denomination early Showa is also often used to cover the first part of Showa reign which was particularly long.
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