Korean Family Titles
외삼촌
oesamchon · Uncle (mother's brother)
Relationship
my mother → her brother
Who uses it
About your mother's brother.
When you call them
Call him 외삼촌 (often just 삼촌 in casual talk). His wife is 외숙모.
When you talk about them
To others, 외삼촌.
Example
외삼촌, 이번 방학에 놀러 가도 돼요?Uncle, can I come visit over the break?
Based on the standard etiquette of the National Institute of Korean Language; families and regions vary.