"Reaction shots" refer to the close-up shots in movies or TV shows that capture the characters' facial expressions or emotional responses to something that just happened. Full definition
You can tell, because the last shot of the film is a dog reaction shot. (filmfreakcentral.net)
His final speech is entertaining but that's as much to do with some clever editing and decent reaction shots from the extras as anything else. (timeout.com)
We added some scenes I loved that I had to cut out, lost other scenes I loved, and used different reaction shots. (awardscircuit.com)