It's One Way GLASS, not mirror
When the reference is to invisible observers, hidden behind a mirror, I think the correct term is One Way GLASS. They can see you, you can't see them = "one way." All mirrors are "one way." Calling something a "one way mirror" is pointless (or senseless). A mirror is completely opaque. Ordinary glass is fully transparent... visibility goes both ways. Hence, normal glass is "two way" glass. On the other hand, ONE way GLASS is something special. See also "semi silvered" or "half silvered glass," which properly configured can offer transparency in only one direction.
Biting the hand that feeds IT
