If you are a girl, this is what you call another girl who is older than you, or a girl who you respect. (Korean term)

Internet persona(s) who happens to follow you and you happen to follow them back and maintain communication with and have a mutual liking for eachother whether it be friendship wise, etc. (Mutuals if more than one mutual)

A Korean term that means older/big sister that females call a female relative or a older girl they a admire or respect. It is sometimes used as a honorific or to replace a person's name.
There are many variations on spelling like Unni, Eonni, Eonnie, Eunni, Eunnie, or onnie. The male version of this term is Nuna or Noona.

a korean's way of calling a close girl part of their family, much more like an older sister(in a girls view)

A Korean honorific/term used by a younger female referring to an older female.

Unnie is the what you call and female who is older than you and you are close with them. THis word is from korean culture so everyone who is a K-Pop stan MUST know this word.