Implicit feedback in human–human conversaton conversation is when small facial or bodil movements, or things we say offer the initial speaker feedback as the wherher they were understood. Explicit confirmation, such as "yes"" or "you said you want a ticket", can be cumbersome. Instead a response such as "which concert would you like a ticket for", provides Implicit feedback that the the second person heard a requtest for atciket, but also carries the conversation forward.
Used in Chap. 19: page 307