What is Bacting?
1.
The art of acting by using your back as defined by Will Ferrell in this video, funnyordie/videos/ac76766583
Note: It's the concatenation of back and acting, bacting.
Bacting occurs when two actors are in the middle of a dialogue and the position of the camera shows the back of an actor and the face of the other actor in the conversation. The expressions made by the back-faced actor is bacting.
See