A succubus is a female demon from old European stories. People used to believe she came to a man while he was sleeping and had sex with him. The male version is called an incubus. This is not a word from everyday life — it comes from medieval religion and folk belief, where it was a serious idea. In the past, people used it to explain things they could not explain: a strange dream, a night when a man woke up frightened and could not move, a man who felt guilty about his own thoughts. Blaming a demon was easier than blaming yourself. Today almost nobody believes in succubi, and the word lives mostly in fantasy books, video games, anime, and role-playing games. There, a succubus is usually drawn as a beautiful woman with small horns, bat wings, and a tail, and she drains a man's life or energy through desire. Because of this, the word now often carries a joking or sexy feeling rather than a frightening one. People also sometimes use it about a real woman, meaning she is dangerously attractive and takes everything from a man — but this is an insult, and quite a strong one, so be careful. The plural is usually succubi (SUK-yuh-by), though succubuses is also used and is not wrong.