also: おう
interjection
Expresses surprise, wonder, or sudden realization. Often drawn out as おおー.
おお、これはすごい！
Oh, this is amazing!
おお、そうだったのか。
Oh, so that's how it was!
interjection
ugh!; oh no!
Expresses dismay, disappointment, or frustration.
おお、また失敗した。
Ugh, I messed up again.
おお、なんてこった。
Oh no, what a mess.
interjection
ah!; the penny drops!
Indicates sudden understanding or realization.
おお、なるほど！
Ah, I see!
おお、そういうことか。
Ah, so that's what it means.
interjection
yes!; okay!
Used as an affirmative response, often in casual or hearty agreement.
「手伝ってくれる？」「おお、いいよ。」
"Can you help me?" "Yeah, sure."
おお、任せてくれ。
Okay, leave it to me.
Emphatic or drawn-out spelling using long vowel mark.
Katakana spelling, often used for emphasis or in manga.
A natural exclamation; the exact origin is uncertain. The kanji 応 is an ateji used for its sound, not its meaning.