The will-o'-the-wisp, sometimes will-o'-wisp or ignis fatuus refers to the ghostly lights sometimes seen at night or twilight — often over bogs. It looks like a flickering lamp, and is sometimes said to recede if approached. Much folklore surrounds the legend, but science has offered several potential explanations.
The term will-o'-the-wisp comes from wisp, a bundle of sticks or paper sometimes used as a torch, and will-o' ("Will of").
The folklore phenomenon will-o'-the-wisp (Will of the wisp) is sometimes referred to as Jack o' lantern (Jack of the lantern), and indeed the two terms were originally synonymous. In fact the names "Jacky Lantern" and "Jack the Lantern" are still present in the oral tradition of Newfoundland. These lights are also sometimes referred to as "corpse candles" or "hobby lanterns", two monikers found in the Denham Tracts. They are often called spooklights or ghost lights by folklorists and paranormal enthusiasts in the United States. Sometimes the phenomenon is classified by the observer as a ghost, fairy, or elemental, and a different name is used. Briggs' "A Dictionary of Fairies" provides an extensive list of other names for the same phenomenon though the place they are observed (graveyard, bogs etc.) influences the naming considerably.
One common scientific explanation for such phenomena is that the oxidation of hydrogen phosphide and methane gases produced by the decay of organic material has been documented to cause glowing lights to appear in the air. Experiments, for example, done by the Italian chemists Luigi Garlaschelli and Paolo Boschetti, have replicated the lights by adding chemicals to the gases formed by rotting compounds.
The names will-o'-the-wisp and jack-o'-lantern refer to an old folktale, retold in different forms across Ireland, Scotland, England, Wales, Appalachia and Newfoundland.
鬼火 (onibi) Japanese for Will o'Wisp, it translates to "ghost/demon fire." It's sometimes associated with or mistaken for the trickster 人魂 (hitodama or "human soul"), blue or green floating balls of fire assumed to be souls of people with unfinished business. Other Japanese myths consider the phenomenon a trick of the kitsune, employing their "fox-fire" (kitsune-bi) to lead travelers astray.