The origine of the phrase "Middle Ages"
The phrase "Middle Ages" has its origins in the fifteenth century. Scholars of the time - primarily in Italy - were caught up in an exciting movement of art and philosophy, and they saw themselves embarking on a new age that revived the long-lost culture of "classical" Greece and Rome. The time that intervened between the ancient world and their own was a "middle" age and, sadly, one they disparaged and from which they disassociated themselves.
Eventually the term and its associated adjective, "medieval", caught on. Yet, if the period of time the term covered was ever explicitly defined, the chosen dates were never unassailable. It may seem reasonable to end the era at the point where scholars began to see themselves in a different light; however, this would assume they were justified in their view. From our vantage point of considerable hindsight, we can see that this was not necessarily the case.
From: "Inventing the Middle Ages" by Norman Cantor and
"The Cambridge Illustrated History of the Middle Ages", edited by Robert Fossier