An anachronism is an inaccuracy of chronology within a piece of literature.  Therefore, if any piece of information (date, time, cultural reference, historical impact, etc.)  is out of place in the timeline of history, then it is an anachronism.  Buy and large, these errors that occur are because of lack of research by the author.  One example of this in literature occurs in Act 2 Scene 1 of William Shakespeare’s play Julius Caesar.  Here, Brutus says, “Peace! Count the clock” and Cassius responds by saying, “The clock has stricken three.”  The time that this play is set in dates back to 44 AD.  The first mechanical clock, was invented in Europe at around the start of the 14th century.  Since this play is taking place back in 44 AD and the clock wasn’t invented yet, the reference Brutus makes is in fact an example of an anachronism.