Today's Meet is just one example of a backchannel.
There are other sites available that can be used as backchannel's,
for example the chat feature in Moodle or itsLearning

From Wikipedia:
Backchannel is the practice of using networked computers to maintain a real-time online conversation alongside live spoken remarks. The term was coined in the field of Linguistics to describe listeners' behaviours during verbal communication, Victor Yngve 1970.

The term "backchannel" generally refers to online conversation about the topic or the speaker. Occasionally backchannel provides audience members a chance to fact-check the presentation.

How do you use Backchanneling in the classroom?

I use backchanneling to facilitate discussion while we watch videos. I have found that students are more engaged when they are watching, discussing, asking, and answering questions all at the same time. Long gone are monitoring students sleeping, passing notes, or distracting others. On the backchannel they are all engaged learners, some providing more insight or better questions than others, but all learning.
Share your backchanneling stories/ideas below.