This is the 350th most frequent Turkish word.
ilçesi
The Turkish word "ilçesi" means "district of" or "its district."
The word 'ilçesi' is used to indicate a specific district ('Beşiktaş'), with the possessive suffix '-i' to show belonging to Istanbul.
İstanbul'un Beşiktaş ilçesi çok hareketlidir.
The Beşiktaş district of Istanbul is very lively.
Here, 'ilçesi' specifies a district within the referred place ('bu il'), emphasizing it as a specific locality.
Bu ilin en güzel ilçesi burasıdır.
This is the most beautiful district of this province.
'İlçesi' refers generally to a district, paired with 'o' (that) to clarify which district is being discussed.