What are those trick mirrors called?

You all know this mirrors from movies. In police stations in the interrogation room. A mirror from one side..see through from the other. Does this foil or mirrors got a specific name? Do they even really exist like they are shown in movies? I googled my *** off but couldn't find good answers or wiki articles. I just found a foil that is not really see through unless there is UV light on the backside..but that's not what its like in movies..so..is this just in movies or do this type of "mirrors" really exist?