also: うふーん
interjection
A light, feminine giggle or chuckle, often used in a coy or playful manner. Mimetic and typically associated with female speech.
彼女は手を口に当てて「うふん」と笑った。
She put her hand to her mouth and giggled, 'Tee-hee.'
interjection
A soft, feminine moan or sigh, often used in romantic or intimate contexts. Mimetic and typically associated with female speech.
彼女は彼の耳元で「うふん」と甘い声を漏らした。
She let out a sweet 'mmh' near his ear.
うふふ is a similar feminine giggle, but often repeated and more sustained, while うふん is a single, shorter utterance.
あはは is a loud, open laugh, not coy or feminine like うふん.
Onomatopoeic or mimetic word; the sound imitates a light, feminine giggle or moan. The exact origin is uncertain.