Short answers, pulled from the story.
The Erinyes were chthonic female deities of vengeance born from the blood of Uranus when Cronus castrated him. Hesiod wrote that this event occurred when Cronus struck his father with a sickle, and Apollodorus confirmed this lineage in later accounts.
Three names became standard for these goddesses: Alecto, Megaera, and Tisiphone. Virgil recognized these specific names when writing the Aeneid, and Dante Alighieri followed this triptych structure in Canto IX of Inferno.
Orestes stood before a jury of Athenian citizens on the Areopagus after killing Clytemnestra to avenge Agamemnon. Athena presided over the trial and cast the deciding ballot for acquittal despite an evenly split vote among jurors.
A sanctuary dedicated to the goddesses stood near the Areopagus hill where Pausanias recorded that Athenians called this place home to the August ones. Images of Pluto, Hermes, and Earth appeared within the shrine walls without terrible features according to ancient observers.
Scholars found the name Erinys written in Mycenaean Greek script on tablets KN Fp 1, KN V 52, and KN Fh 390 from the Bronze Age period of Greece. Robert Beekes suggested the word has Pre-Greek origins connected with verbs meaning to raise or stir up strife.