/ˈʌndərˌɡraʊnd sɛl/ – Phrase
Definition: hầm giam.
A more thorough explanation: “Underground cell” typically refers to a clandestine or secret group or organization that operates covertly, often engaging in illegal or subversive activities. In a legal context, an underground cell may be associated with criminal activities such as terrorism, organized crime, or insurgency.
Example: The suspect was held in an underground cell while awaiting trial.