Simple Definition of anachronism:
: something (such as a word, an object, or an event) that is mistakenly placed in a time where it does not belong in a story, movie, etc.
: a person or a thing that seems to belong to the past and not to fit in the present
Full Definition of anachronism:
1: an error in chronology; especially : a chronological misplacing of persons, events, objects, or customs in regard to each other
2: a person or a thing that is chronologically out of place; especially : one from a former age that is incongruous in the present
3: the state or condition of being chronologically out of place
definition from Mirriam-Webster