A spoiler is information that reveals a surprise or important plot point in a story before you experience it yourself. When someone tells you the ending of a movie you haven't seen yet, they're spoiling it for you. If a friend announces who the villain turns out to be in a mystery novel, that's a spoiler.

The word comes from the idea that this information spoils your experience, like how spoiled milk ruins what should be fresh and good. Discovering plot twists yourself creates excitement and surprise, but spoilers take that discovery away. When you know the hero's secret identity before reading the book, or when you learn who wins the championship before watching the game, the tension and suspense disappear.

People often warn “Spoiler alert!” before discussing plot details, giving others a chance to cover their ears, look away, or walk away. Some people don't mind spoilers at all and actually enjoy knowing what happens in advance. Others feel genuinely upset when a story gets spoiled for them.

In a completely different context, a spoiler is also an aerodynamic device on a car or airplane. On race cars, a spoiler is that wing-like piece on the back that pushes the car down onto the road at high speeds, helping the tires grip better. On airplanes, spoilers are panels that pop up on the wings to slow the aircraft down after landing.