23 special wards (特別区; Tokubetsuku) are special districts in Tokyo, Japan. Each ward is about the size of an urban zip code (i.e. Manhattan would probably have about 10 ku in it). Those wards in terms of size are distinguished from ku in other large cities in Japan.
One of Tokyo's names (understood throughout Japan) is nijūsanku (２３区), simply meaning "23 wards". This refers specifically to inner Tokyo, as opposed to the entire expanse of Tokyo prefecture, which stretches from remote mountain villages in the west to the Ogasawara Islands 1000 km to the south.
The 23 wards are: