An adverb meaning 'really' or 'truly', used to state reality or to emphasize surprise or strong feeling.
本当にありがとう。君が来てくれて助かったよ。
Thank you so much. You coming really helped me.
彼が優勝したって？本当に？信じられないよ。
He won the championship? Really? I can't believe it.
この料理は本当においしい。レシピを教えてください。
This dish is really delicious. Please tell me the recipe.
本当に疲れたから、今日は早く寝るつもりだ。
I'm really tired, so I plan to go to bed early today.