保密线人：指在调查过程中为执法部门提供关键信息的人，通常这些信息有助于破案或揭示犯罪活动。保密线人的身份通常是保密的，以确保他们的安全。
告密者；秘密线人
The authorities receiving the report shall keep confidential the relevant information of the informant, and protect the legitimate rights and interests of the informant.
接受举报的机关应当对举报人的相关信息予以保密，保护举报人的合法权益。
The authority or organ that accepts such information shall keep the informant as well as the contents of such information confidential.
接受举报的机关应当对举报人和举报内容保密。
The identity of the informant shall be kept confidential.
前项通报人之身分资料应予保密。
Solomon Barnes, whose confidential informant, along with undercover deputies, placed bets on youth football during the police investigation.
FORBES: Coaches Among Those Arrested in South Florida Youth Football Gambling Case
The FBI used a confidential informant to record the group's meetings.
Mr Mathis explains in an affidavit how Carty acted as a confidential informant for him and that he would have spoken in Carty's defence had he been asked.