오빠
Oppa
What does it mean?
A woman uses 오빠 for her older brother. She may also use it for an older male friend or partner when they are close enough.
How it sounds
A: 오빠, 이것 좀 봐. B: 왜?
When do Koreans use it?
It is relationship-based, not a general word for any attractive older man. The speaker is female and the man is older than her.
A small nuance
Tone and relationship matter a lot. In dramas it may sound romantic, but in real life it can be completely familial or friendly.