diplomatic mission; representative office
Refers to an official office representing a country or organization abroad, such as an embassy, consulate, or permanent mission.
Japan maintains a diplomatic mission at the United Nations.
I work at the Permanent Mission of Japan in Geneva.
領事館 means 'consulate', a type of diplomatic mission focused on consular services; 代表部 is a more general term that can include consulates but also other representative offices.
Compound of 代表 (daihyō, 'representation') + 部 (bu, 'department, office'). The term is used in modern Japanese for official representative offices, particularly in diplomatic contexts.