A devil is an evil spirit or demon in many religions. In Christian tradition, the Devil (often called Satan) is the most powerful evil spirit, who rebelled against God and now tempts people to do wrong. When people talk about the devil, they usually mean this specific figure: the enemy of goodness who tries to lead people into evil.

People use devil more casually too. Someone might call a mischievous person a “little devil” if they're playfully naughty. If you're caught between two difficult choices, you might say you're “between the devil and the deep blue sea.” When someone plays devil's advocate, they argue for an unpopular position just to test an idea, not because they actually believe it.

The phrase “speak of the devil” means someone appears right when you're talking about them. If you're discussing your friend Maya and she suddenly walks into the room, you might say “speak of the devil!” It's just a playful expression, not actually calling someone a devil.