The term "Dark Ages" is a historical label traditionally applied to the early medieval period in Europe, following the fall of the Western Roman Empire in 476 AD. In its broadest usage, the term covers roughly the 5th to 15th century, overlapping with what historians more precisely call the Middle Ages or Medieval Period.
The label originated with the Italian scholar Petrarch in the 14th century, who used it to contrast the perceived cultural and intellectual decline of the post-Roman period with the achievements of classical antiquity. The "darkness" referred to a supposed lack of literary, scientific, and cultural advancement, as well as the relative scarcity of written historical records from the period compared to the classical era.
Modern historians generally avoid the term because it oversimplifies a complex period that included significant developments in art, architecture (such as Gothic cathedrals), philosophy (scholasticism), and technology. When used at all today, it is more often restricted to the early medieval period (roughly 5th to 10th century), but in examination contexts the broader span of the 5th to 15th century is the standard answer.
The Renaissance period (roughly 14th to 17th century) is understood as the era that followed and replaced the "Dark Ages." The 1st century was part of the Roman Empire's peak, and the Industrial Revolution occurred in the 18th and 19th centuries.