During winter darkness, the sun never rises above the horizon. This occurs in polar regions for parts of the winter. The closer you are to the poles, the more days you have with winter darkness. Like with ordinary twilight, we can classify winter darkness by how many degrees below the horizon the sun rises at its highest. For example, a polar night is >6° below the horizon. Winter darkness does not mean complete darkness 24 hours a day. Some say we should rather name it winter colouring because the light from the sun below the horizon is reflected in so many various spectra. Regions with winter darkness have an equally long period of midnight sun during summer.
Foto: Although the sun does not rise above the horizon during winter darkness, some of its light is reflected so that it is seldom completely dark during daytime. This is Bjørndalen near Longyearbyen at midday 4th of February. Photo copyright: Bjørn Frantzen, NIBIO.