Korean Family Titles
친할머니
chinhalmeoni · Grandmother (father's mother)
Relationship
my father → his mother
Who uses it
About your father's mother.
When you call them
Face to face, simply 할머니.
When you talk about them
To others, 친할머니 when you need to say which side; recent etiquette guides suggest you needn't add 친 at all.
Example
할머니, 저 이번 시험 잘 봤어요!Grandma, I did well on my exam!
Based on the standard etiquette of the National Institute of Korean Language; families and regions vary.