A demon is an evil spirit or supernatural being that appears in the religious traditions and folklore of cultures around the world. In Christian belief, demons are fallen angels who rebelled against God and now work to tempt or harm humans. In other traditions, demons might be mischievous spirits, monsters, or creatures that cause trouble and suffering.

The word often appears in stories and legends where heroes must face demonic enemies. In ancient Greek tales, a daemon (pronounced differently) wasn't necessarily evil but simply a spirit or divine power, though over time the word came to mean specifically evil beings. Medieval stories featured knights battling demons, and many cultures have their own versions, such as the oni of Japanese folklore, the djinn of Middle Eastern tales, and countless others.

People use the word figuratively too. Someone might describe their inner demons when talking about personal struggles or fears they're battling. A coach might say a player needs to exorcise their demons after a string of losses, meaning they need to overcome whatever is holding them back. In this sense, a demon represents any persistent difficulty that haunts someone.

The word appears frequently in fantasy books, video games, and movies where characters encounter supernatural evil forces. A demonic presence suggests something frighteningly evil or otherworldly.