I added a new page on this site found on the right side. Its the Kinship Terms or how to address family members or related person. Just like how Korean uses different styles in communicating (formal, formal-polite and intimate), addressing people may also varies depending on the gender of the person related. There are also honorifics used for esteemed person (person of higher social status).
I know a lot of Korean movie and drama fanatics are used to hearing 오빠 (oppa), 누나 (nuna) or 언니 (eonni). Thesea re just some of the terms used to denote relationship which at times are not limited to blood relations. 오빠 can be used by a younger girl to call her boyfriend or old friend who is a guy. Same goes with 누나, this is not limited to an older sister to a younger brother but can be used to address older girls close to a guy.
To know more about this, check out the page on Kinship Terms.