/ˈʌndərkʌvər ˈpɜːrtʃəs/ – Phrase
Definition: thủ đắc bí mật.
A more thorough explanation: An undercover purchase refers to a transaction in which a law enforcement officer or agent poses as a regular consumer in order to gather evidence of illegal activity, such as the sale of contraband or illicit goods.
Example: The undercover purchase of illegal drugs led to the arrest of several individuals involved in the drug trafficking operation.