back channel

noun5

1. •
   A secondary channel of activity, typically in parallel with primary channels and somewhat independent of them.
2. •
   An unofficial communications channel used to make informal or subversive negotiations.
3. •
   A real-time online discussion that occurs simultaneously with a verbal presentation.

   • TodaysMeet visualizes collaborative and parallel conversations in a backchannel through a digital classroom where every student has a voice. — 2017
4. •
   A gesture or short prompt by which a listener invites a speaker to continue.
5. •
   The smaller of two channels in a river that diverge to form an island.