witness protectionnoun [ U ]
uk/ˌwɪt.nəs prəˈtek.ʃən//ˌwɪt.nəs prəˈtek.ʃən/methods of protecting someone who may be in danger as a result of agreeing to tell the courts or police what they know about a crime:
an expert in witness protection
US also witness protection program, UK also witness protection programme, witness protection scheme [ C ] a system in which someone who has agreed to tell the courts or police what they know about a crime is protected, usually by preventing their address and identity from becoming known:
The FBI told Cullotta that Spilotro had ordered a hit on him, and Cullotta entered witness protection.
Brennan and his family were put into a witness protection programme with new identities.