A nickname for the devil, used by sailors. He is sometimes seen as a seperate entity. Commonly associated with the bottom of the sea, known as Davy Jones' Locker.
"This same Davy Jones, according to the mythology of sailors, is the fiend that presides over all the evil spirits of the deep, and is often seen in various shapes, perching among the rigging on the eve of hurricanes, ship-wrecks, and other disasters to which sea-faring life is exposed, warning the devoted wretch of death and woe." ~Tobias Smollett