The Sublime Porte, also known as the Ottoman Porte or High Porte, was a synecdoche or metaphor used to refer collectively to the central government of the Ottoman Empire in Istanbul.
The Imperial Gate (Bâb-ı Hümâyûn), leading to the outermost courtyard of Topkapi Palace, was known as the Sublime Porte until the 18th century.
The later Sublime Porte proper in 2006
Synecdoche is a type of metonymy; it is a figure of speech in which a term for a part of something is used to refer to the whole, or vice versa. The term is derived from Ancient Greek συνεκδοχή (sunekdokhḗ) 'simultaneous understanding'.
A common example of synecdoche: using the term boots to mean "soldiers", as in the phrase "boots on the ground".