backchannel
/ˈbæktʃænəl/noun
1- a secondary or covert route for the passage of information（信息传递的）秘密渠道：
have used him as a diplomatic backchannel
曾利用他作为秘密外交渠道
as modifier backchannel reports.秘密渠道的报道。
1.1
- Psychology a sound or gesture made to give continuity to a conversation by a person who is listening to another【心理】反馈。