What is "pleistos"

The Pleistos (, ) is a river in central Greece. It rises at Mount Parnassos near the town Arachova, Boeotia. It flows west through a deep valley, between the mountains Parnassos and Kirphe, passing south of Delphi, through the Delphic Landscape and the plain of Amphissa and flows into the Corinthian Gulf near Kirra. The water of the Castalian Spring flow into Pleistos.