Ōoku

The Ōoku (大奥, great interior^?) refers to the harem of Edo Castle, the section where the women connected to the reigning Shogun resided. Similar areas in the castles of powerful Daimyo, such as the Satsuma Domain, were also referred to by this term.

This included the shōgun's mother, wife, and concubines. Rumored to house several thousand women, including maids and servants at one point, the Ōoku was, as much as any other part of Edo Castle, a focal point of political intrigue for the Tokugawa shogunate.

There were no male adults admitted onto the floor of the Ōoku without the Shōgun. The corridor through which the Shōgun entered was called Osuzu Rōka (御鈴廊下^?, large corridor of the bells), derived from the ringing of the suzu bells to announce the entrance of the Shōgun. This corridor was the only route which connected the Ōoku to rest of Edo Castle, and it was usually locked.

Later, a second corridor was built as the escape route against disasters such as fires or earthquakes.

A lady in the rank of an Otoshiyori (御年寄^?) or Jōrō Otoshiyori (上臈御年寄^?) or the senior ladyship held the reins of power in the Ōoku, while attaining the influence equivalent to a Rōjū in Edo Castle.

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Wikipedia