A maniac is someone who acts in a wild, frenzied, or reckless way, often without thinking about consequences. When your little brother runs around the house shrieking and jumping off furniture, someone might call him a little maniac. When a driver speeds dangerously through traffic, weaving between cars, you might say they're driving like a maniac.

In everyday conversation, calling someone a maniac usually just means they're acting wild, intense, or out of control in that moment. A soccer maniac loves the sport so intensely they watch every game and know every statistic. A cleaning maniac scrubs everything obsessively until it sparkles.

Sometimes maniac appears in phrases like raving maniac, which describes someone extremely wild or out of control. But most of the time, it's used with exaggeration or humor: “My dog is a maniac when the doorbell rings” or “The fans went maniacal when their team scored.”

The related word maniacal means wild and frenzied, like maniacal laughter from a cartoon villain.