code word
US /ˈkoʊd wɜːrd/
UK /ˈkoʊd wɜːrd/

1.
暗語, 口令
a word or phrase that has a secret meaning and is used to give a message or signal
:
•
The spies used a specific code word to identify each other.
間諜們使用特定的暗語來識別彼此。
•
Only those who knew the code word were allowed to enter.
只有知道暗語的人才被允許進入。