noun
United Nations Secretariat
Refers specifically to the administrative organ of the United Nations, headed by the Secretary-General.
国連事務局はニューヨークに本部を置いている。
The United Nations Secretariat has its headquarters in New York.
国際連合 is the full name for the United Nations as a whole, while 国連事務局 refers specifically to its Secretariat.
Compound of 国連 (abbreviation of 国際連合 'United Nations') + 事務局 ('secretariat').