Ida Green is the mother of Dr. Leonard Green and the paternal grandmother of Amy, Rachel and Jill Green. This relationship makes her the great grandmother of Rachel's daughter, Emma Geller-Green. She is an unseen character on the show; she is mentioned in The One With Rachel's Phone Number when Phoebe and Rachel go out to a bar and meet two guys who live in her building.
Apparently, she smells like potatoes so the people who lived in her building nicknamed her "Spuds".