An oppa can be an:
Real biological older brother
A male friend who is older than the woman
An older male a girl is trying to flirt with
"Ye Jin ah! How dare you speak my name"
"Yeh oppa" *puts head down in shame*
Usually used in the annoying way by crazy kpop or jpop fangirls.
"Oppa is so Kawaii~<3"
"SHUT THE HELL UP, WOMAN!"
It's often used in a romantic relationship when a girl refers to her boyfriend (or the girl hitting on a guy) who is older/same age as her.
Oppa literally means "older brother"
The male version of this word is hyung.
I told oppa that I'll come home early today.
2. sign you're talking to a white kid who thinks appropriating Asian culture is cool and not offensive cause they're into K-Pop and J-Pop. Often paired with an adjective ("one sexy oppa" = hot guy, "curdled milk oppa" = ugly guy, etc.)