What did you call your grandparent(s)?

One of my favorite thing to learn about people is the names they had for their grandparents. While Grandpa and Grandma are certainly the most popular/common ones, I feel like grandparents get the craziest/most awesome nicknames from their grandkids.

There's nothing funnier to me than people who served in World War II or raised 14 kids during The Great Depression being called, like, Gum Gum and Pee Paw instead of their real, distinguished names. So, what did you call your grandparent(s) and how did the name come to be?

Anyway, love you Grammy and Pop-Pop!