/ˈʌndərˌɡraʊnd prɛs/ – Phrase
Definition: các tờ báo hoạt động bất hợp pháp hoặc không chính thống.
A more thorough explanation: illegal newspapers, magazines or journals etc, especially ones published in a place where certain publications are forbidden or highly censored
Example: He began working for the underground press in the late-1960s .