the period from about the late 5th century ad to about 1000 ad, once considered an unenlightened period
2.
(occasionally) the whole medieval period
Dark Ages in American English
the Middle Ages, esp. the earlier part from about a.d. 476 to about the end of the 10th cent.: so called from the idea that this period in Europe was characterized by intellectual stagnation, widespread ignorance and poverty, and cultural decline