Terribly means extremely or very much, though the word originally meant “in a way that causes terror.” Today, we use it in two main ways that sound opposite but both mean “very.”

When something goes terribly wrong, it goes badly: “The picnic went terribly when it started pouring rain.” A student who does terribly on a quiz performs poorly.

But here's where English gets interesting: we also use terribly to intensify positive things. “I'm terribly excited about the field trip” means extremely excited. “She's terribly clever” means very clever indeed. When someone says “I'm terribly sorry,” they're expressing deep regret, not saying their apology is bad.

This double use can confuse people learning English. The key is context: terribly usually means “very badly” when describing performance or outcomes, but “very much” when describing feelings or qualities. You might be terribly disappointed (very disappointed) about doing terribly (very poorly) on something. The word adds emphasis either way, turning ordinary statements into stronger ones.