Korean Family Titles
큰아버지
keunabeoji · Uncle (father's older brother)
Relationship
my father → his older brother
Who uses it
About your father's older brother.
When you call them
Call him 큰아버지; his wife is 큰어머니.
When you talk about them
To others, 큰아버지 or 백부 (formal).
Example
추석엔 큰아버지 댁에 다 모여요.On Chuseok, everyone gathers at my eldest uncle's house.
Based on the standard etiquette of the National Institute of Korean Language; families and regions vary.