Who is Periamma. from Climbing the Stairs and what is their importance?

Periamma is the wife of appa's older brother. Periamma is a title, not a name. She is in charge of Thatha's home, and she is described as an unkind, jealous, cruel, and boosy woman, who refers to appa as "the idio." She likes to gossip and goes out of her way to show her power.