Proper noun
(literally) The monumental portal at the Ottoman palace where the supreme tribunals were held; became the surname of the first palace in Bursa, transferred to the even grander Topkapı palace after the capital's transfer to Istanbul (the former Byzantine imperial capital Constantinople)
(figuratively) A pars pro toto for the Ottoman sultanic court, hence for the imperial government, notably the vizierial divan and the entire empire, or a personage with a similar standing.
Source: en.wiktionary.org