Informant的英文释义为：a person who gives secret information about sb/sth to the police or a newspaper，表示“检举人，举报人，线人”，指检举或告发他人者，尤指秘密向警方提供有关犯罪情况或信息的人，有时可以以此换取一定报偿或某种特别待遇。也称informer或feigned accomplice。比如informant survey知情人调查。key informant关键检举人，关键知情人。informant center举报中心。

参考例句：These include records relating to enforcement of the criminal law where the subject is not aware of the investigation and disclosure of the record could reasonably be expected to interfere with enforcement proceedings, records maintained by a criminal law body under an informant’s name, unless the status of the informant is public, and records maintained by the Federal Bureau of Investigation pertaining to foreign intelligence or international terrorism.

这些例外包括：与刑事执法相关的记录，当事人并未意识到正被调查，而披露该记录自然可能妨碍执法行动；刑法机构以线人的名义保留的记录，除非该线人的状况已经公开；以及由联邦调查局所保留的有关外国情报或国际恐怖主义的记录。

The word “witness” shall mean anyone who has provided evidence or testimony, or will provide evidence or testimony, or who describes specific events that he witnessed; the protective measures shall be extended to all members of the family of an informant or witness and to members of his household.

证人”指的是已经提供证据或证词或即将提供证据或证词的人，或描述亲眼目睹具体事件的人；应向检举人或证人的所有家庭成员及共住家庭成员提供保护措施。