medieval
The Medieval period (also known as the Middle Ages) was a time period in Europe that lasted for 1000 years, from the end of classical antiquity (conventionally dated to the fall of the Western Roman Empire in 476) until the early modern period around 1500 (roughly coinciding with the widespread use of the printing press and the discovery of the New World). Today, the Middle Ages are synonymous with knights and high fantasy aesthetics.
At Danbooru, this tag should be used for fashion that the typical Western audience would consider to pertain to this era, such as knight's armor, gowns with long sleeves, laced sandals, boots, and even cloaks. It also covers pre-modern European architecture such as castles.
This should not be confused with the Renaissance period, which came after/during the Late Middle Ages and marked the onset of early modern era.