1. What does it mean?
ㅎㅎ uses repeated ㅎ letters to suggest laughter, often a light chuckle rather than a loud reaction. It can accompany a friendly acknowledgment or soften the ending of a message.
Also written or said as ㅎㅎㅎ, ㅎㅎㅎㅎ, 흐흐, hahaha
2. The nuance
It is not automatically polite, romantic, or passive-aggressive. Those readings depend on the sentence and relationship. It can appear next to polite grammar, but does not replace an appropriate greeting or apology.
3. Examples
“추천한 빵 먹어 봤어. 진짜 부드럽더라 ㅎㅎ”
I tried the bread you recommended. It was really soft, hehe.
“사진 보내 줘서 고마워 ㅎㅎ 잘 간직할게.”
Thanks for sending the photo. I'll keep it safe. :)
Sources
FluentU: Korean text slang guide
References support the meaning and usage. Example sentences are written for NoCapWiki.