Most people learn the words 오빠, 언니, 형, and 누나 during the low-beginner level, or even before they've begun properly learning Korean. They can be used to refer to your older siblings (older brother, older sister). However, whether you're a boy referring to your older brother or sister, or if you're a girl referring to your older brother or sister, you'll have to use a different word.
But that doesn't mean that males can't also say 오빠 and 언니, or that females can't say 형 and 누나. Never heard of this before? Find out here.
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