Darkness is the absence of light, but earlier in history it was sometimes viewed as a substance in its own right, and appears in this form in some fantasy literature. Another name for darkness in this context is shadow.

As a metaphor, it is also the lack of knowledge (ignorance). It is also associated with mystery and with unknown things.

In Western tradition, darkness is also associated with evil, evil entities (such as demons or Satan), and Hell or, especially in Egyptian mythology, the underworld. This concept can be seen personified in the character of Darkness played by actor Tim Curry in the 1985 fantasy movie Legend, where Darkness takes the form of a 15 foot high stereotype of Satan, complete with reddened skin, long horns and cloven hooves. The darkness was also an important part of gnostic religious systems; it was usually associated with evil. According to the gnostics, the world is the result of a fight between the darkness and the light.