Have you ever been watching a tv show or movie and notice something that does not belong for the time period that the show is set.
These are called an anachronism.
a thing belonging or appropriate to a period other than that in which it exists, especially a thing that is conspicuously old-fashioned.
One such show that we watvh that have used this a number of times is Murdoch Mysteries (good show). So next time you find yourself doing a double-take or wonder why one of these things is not like another then it just might be an anachronism.