A dream vision or visio is a literary device in which a dream or vision is recounted as having revealed knowledge or a truth that is not available to the dreamer or visionary in a normal waking state. While dreams occur frequently throughout the history of literature, visionary literature as a genre began to flourish suddenly, and is especially characteristic in early medieval Europe. In both its ancient and medieval form, the dream vision is often felt to be of divine origin. The genre reemerged in the era of Romanticism, when dreams were regarded as creative gateways to imaginative possibilities beyond rational calculation.
Source: Dream vision – Wikipedia