To trounce someone means to defeat them decisively and overwhelmingly. When one basketball team trounces another 98 to 45, they dominate the entire game from start to finish. When a chess champion trounces an opponent, the match isn't even close.

The word carries a sense of total victory, not just a narrow win. If you beat your friend at a video game 101 to 99, you won, but you didn't trounce them. But if you beat them 150 to 20, that's a trouncing. The word suggests the winner was so much better that the outcome was never really in doubt.

You'll often see trounce used in sports reporting (“The home team trounced their rivals”) or when describing one-sided debates, elections, or competitions. There's something almost cheerful about the word itself: it sounds bouncy and energetic, even though getting trounced isn't much fun for the losing side.