federal district

Short definition from Wiktionary

Noun

1. 1
   A type of federal subdivision, often composed of a capital city.
2. 2
   In Russia, a grouping of federal subjects (top-level administrative divisions), created for the purpose of ensuring compliance of the containing federal subjects with national law.

Proper noun

1. 1
   An administrative division of Brazil; located in the Center West Region of Brazil and containing the country's capital Brasilia
2. 2
   Before 2016, the name formally given to Mexico City, the country’s capital.