Naishi was a kind of female government post in Japan before the Modern era. Naishi means as below.
A collective name for the court ladies served in Naishi no tsukasa (female palace attendants) that was the government office in the women's quarters of the Imperial Palace.
A kind of the court lady served in Saigu-ryo (the Bureau of the High Priestess of Ise).
A kind of the court lady served in Saiinshi (Office of the High Priestess of Kamo-jinja Shrine).
A shrine maiden of Itsukushimajinja shrine in Aki Province.
Naishi in Naishinotsukasa
Naishi was a collective name given to the court ladies who attended on the emperor; their official duties included conveying reports to the emperor and passing on imperial decrees to retainers. Naishi adopted the Shitokan system such that Kami was called Naishinokami or Shoji (the prescribed number was two), Suke was called Naishinosuke or Tenij (the prescribed number was four), and Jo was called Naishinojo or Shoji (the prescribed number was four), without the post of Sakan. Gon no naishinojo (the prescribed number was two) was sometimes placed, and 'Naishidai' was temporarily appointed to substitute Naishi during her menstruation. Naishidai' was placed in Togubo and immediately promoted to Naishi after the enthronement of the Crown Prince.
For further details, see 'Naishi no kami.'
Naishi no suke always attended on the emperor, and held out Kenji when the emperor went to the annex. A wet nurse of the emperor was appointed Naishi no suke in most cases, in which Naishi no suke served as a messenger in the ceremony Yasoshima matsuri which took place after the enthronement.
When the emperor abdicated the throne in favor of his successor, Naishi no suke handed on Kenji to Konoenojisho as her duty (the duty was called 'Okurinaishi'), which was later took over by an experienced Naishi no jo 'Koto Naishi.'
Naishi no jo
Naishi' in a narrow sense solely meant Naishi no jo.
Naishi of Saiguryo
Naishi attended on Saigu and looked after her.
Naishi of Saiinshi
Similar to Naishi of Saiguryo, Naishi of Saiinshi attended on Saiin and look after her.
Naishi of Itsukushimajinja shrine
Naishi was the female priest (shrine maiden) of Itsukushimajinja shrine, being in charge of not only the religious services but also do some performances including singing Imayo song and showing a bugaku dance to relieve a nobleman who was confining himself in the shrine for prayer from the tedium of a journey. The Article of 'Shake guso naishi narabi shoyakunin shinnin no na' of "Itsukushima michishibaki" lists up the names of Naishi from the first rank to the eighth rank and commented that they were called 'Yaotome' and 'Honnaishi'; it is said that there were more than dozen of Naishi under the names of 'Wakin Naishi', 'Karakami Naishi' and the like. Incidentally, Mikohimegimi, who was the seventh daughter of TAIRA no Kiyomori and became a consort of Emperor Goshirakawa, is said to be a child between Kiyomori when he was Aki no kami and Naishi of Itsukushimajinja shrine.