In my dotage, or vigilance, as I like to think of it, I have occasionally railed against the notion of backchanneling, e.g. here and here and here. But hey, if this is the future, who am I etc?
Now the superb Educause Learning Initiative series "7 Things You Should Know" addresses this concept - so repugnant to old-school geezers like me - in an attractive 2-pager. Here's a summary, certainly much fairer than anything I could muster. ("add another dimension to learning" - yeah, right):
Backchannel communication is a secondary conversation that takes place at the same time as a conference session, lecture, or instructor-led learning activity. This might involve students using a chat tool or Twitter to discuss a lecture as it is happening, and these background conversations are increasingly being brought into the foreground of lecture interaction. Digital technologies allow background discussions—which have always been a component of classes, conferences, and presentations—to be brought out of the shadows and, perhaps, incorporated as a formal part of learning activities. Instructors and presenters alike should be aware of this dynamic and the opportunity it presents to add another dimension to learning.