1A casual affirmative response used to show agreement — an informal counterpart to はい.
「今日は暇？」「うん、暇だよ。」
"Are you free today?" "Yeah, I'm free."
母に聞かれて、うんと頷いた。
When my mother asked, I nodded and said "uh-huh."
「一緒に行く？」「うん、行く行く。」
"Want to come along?" "Yeah, I'll come."
2A sound made while thinking or hesitating — similar to "hmm" or "well," expressing consideration.
「うーん、どっちがいいかな。」と彼はしばらく考えた。
"Hmm, which one is better..." he thought for a while.
質問されて「うん…」と言葉に詰まった。
When asked the question, I hesitated and went "um..."
3A short groan let out when enduring pain or discomfort.
荷物を持ち上げた瞬間、彼は「うん」と小さくうめいた。
The moment he lifted the load, he let out a small groan.