will-o'-the-wisp_(mythology)

A will-o'-the-wisp (also known as ignis fatuus, Latin for "foolish fire") is a ghostly blue-green flame appearing at night with no apparent source. The name is a combination of the male first name "Will" and the word "wisp", meaning "bundle of hay or straw used as a torch". Thus the name in full means "Will of the torch", making it a counterpart to jack-o'-lantern, or "Jack of the lantern".