Monica and Ross’s grandmother Nana was named Althea.
Althea is the maternal grandmother of Ross and Monica Geller on Friends. She is best remembered from “The One Where Nana Dies Twice,” the first-season episode in which the family gathers after Nana is believed to have died. The title’s joke comes from the episode’s comic misunderstanding: Nana appears to die, then briefly seems to revive, before dying again.
The episode also establishes the Geller family’s emotional and comedic dynamic. Ross is uncomfortable confronting death, while Monica is especially affected by Nana’s condition and by the family gathering around her. Their grandmother’s name is later reinforced through a trivia question in “The One with the Embryos,” when the friends compete in a quiz game involving personal facts about Monica and Ross.
Althea is sometimes confused with other older Geller relatives, including their grandmother’s sisters and aunts mentioned elsewhere in the series. The canonical answer to the question about Nana’s first name is Althea, and she is identified as Monica and Ross’s maternal grandmother.