A demon is a malevolent supernatural entity. Historically, belief in demons, or stories about demons, occurs in folklore, mythology, religion, and literature; these beliefs are reflected in media including comics, fiction, film, television, and video games. Belief in demons probably goes back to the Paleolithic age, stemming from humanity's fear of the unknown, the strange and the horrific. In ancient Near Eastern religions and in the Abrahamic religions, including early Judaism and ancient-medieval Christian demonology, a demon is considered a harmful spiritual entity that may cause demonic possession, calling for an exorcism. Large portions of Jewish demonology, a key influence on Christianity and Islam, originated from a later form of Zoroastrianism, and was transferred to Judaism during the Persian era.

Supernatural refers to phenomena or entities that are beyond the laws of nature. The term is derived from Medieval Latin supernaturalis, from Latin super- + natura (nature). Although the corollary term "nature" has had multiple meanings since the ancient world, the term "supernatural" emerged in the Middle Ages and did not exist in the ancient world.