Who are the Furies?
The Furies torment Orestes
Red-figure vase from South Italy ca. 380 BC
(Naples Archaeological Museum)
In Greek mythology, the Furies were terrifying female spirits of the underworld who frightened men when they had done something bad. Greek men called them the Erinyes, "the angry ones". They were like the voice of your conscience, or the anger of dead people.
Like Aphrodite, the Erinyes were born out of the blood when Kronos wounded his father Ouranos. You could say that Aphrodite and the Erinyes are two sides of the same coin - love and hate. Like everything the Greeks associated with women, the Earth and the underworld, the Furies carried snakes.
Greek men were so scared of the Furies that they usually didn't even call them "the angry ones", but instead called them the Eumenides, "the nice ones," hoping that this would calm the spirits down, like how people say, "Nice dog" as the dog is growling at them.
The most famous appearance of the Furies in Greek myth is in the story of Orestes, who was pursued by the Furies after he murdered his mother.
D'aulaire's Book of Greek Myths, by Edgar and Ingri D'Aulaire.
Greek Religion, by Walter Burkert (reprinted 1987). By a leading expert. He has sections on each of the Greek gods, and discusses their deeper meanings, and their function in Greek society.