From Zelda Wiki, the Zelda encyclopedia
Anju's Mother (daughter in law)
"Gampy" is a character mentioned in Granny's Diary in Majora's Mask during the Final Day, but he never makes an in-game appearance. Gampy is Granny's late husband and the father of Tortus. The diary mentions that Granny, Anju, and Anju's Mother will be taking refuge at Romani Ranch, and goes on to say that she will take several of Gampy's favorite books along with her.
The Japanese text refers to "Gampy" as "grandfather" (おじいさん). "Gampy" then could be derived from the word "Grandpa".