To overact means to perform with too much emotion or drama, making your actions seem exaggerated and unnatural. When actors overact in a play or movie, they might make ridiculously big facial expressions, speak in an overly dramatic voice, or gesture wildly when a simple movement would work better. Instead of seeming like a real person, an overacting actor looks fake and can be accidentally funny.

You can overact outside of theater too. If someone drops their pencil and you gasp loudly, clutch your chest, and exclaim, “Oh no! How terrible!”, that is overacting. The situation doesn't call for that much drama.

The opposite of overacting is underacting, where someone barely shows any emotion at all. The sweet spot is right in the middle: showing genuine feeling without going overboard. When you're telling a story about something exciting that happened, you want your listeners to believe you and stay interested. If you overact, they might think you're being silly or dishonest.