Will-o'-the-wisp

The will-o'-the-wisp or ignis fatuus, or in plural form as ignes fatui ("fool's fire(s)") refers to the ghostly lights sometimes seen at night or twilight that hover over damp ground in still air — 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.
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Noun
1. a pale light sometimes seen at night over marshy ground
(synonym) friar's lantern, ignis fatuus, jack-o'-lantern
(hypernym) light, visible light, visible radiation
2. an illusion that misleads
(synonym) ignis fatuus
(hypernym) illusion, fantasy, phantasy, fancy

(n.)
See Ignis fatuus.
  

[Folklore] Will-o'-the-wisps are the faint lights seen on marshes and bogs on still nights after sunset. Usually a soft bluish light, but also reddish or greenish in appearance. In folklore, they are thought to be imps or pixies leading victims to danger in swamps and heaths. Sometimes they are believed to be the spirits of stillborn children flitting between heaven and hell. It is also known as Jack O'Lantern, Peg-a-Lantern, Friar's Lantern, Spunkie, Fox Fire, and Walking Fire. The classical name for this phenomena is Ignus Fatuus ("fools fire").

FUOCO FATUO. PERSONA INAFFERRABILE