diplomatic bag
noun🔊/ˌdɪpləˌmætɪk ˈbæɡ/
🔊/ˌdɪpləˌmætɪk ˈbæɡ/
(British English) (US English diplomatic pouch)
a container that is used for sending official letters and documents between a government and its representatives in another country and that cannot be opened by customs officers 外交邮袋，外交信袋（海关官员不能拆封）