I've heard it talked about in the past. I think it is where transparent orange tinted screens are put up over the windows. The instructor can see through them for lookout, etc. The student puts a pair of polarised glasses on, orientated 90 degrees out of phase to the screens. The result is that the student cannot see through the screens, but can see the instruments. The instructor can see everything.
Sounds much better than a hood. No cheating!