Latin: Ignis fatuus, 'Foolish fire'
Corpse candles, Elf light, Fairy light, Fox fire, Friar's lantern, Hinkypunk, Hobbedy's lantern, Hobby lantern, Jack-o'-lantern, Liekkiö, Night whispers, Will-o'-wisp, Wisp

A will-o'-the-wisp or ignis fatuus is a ghostly light sometimes seen at night or twilight, dancing over bogs, brakes swamps, marshes, and water meadows. It resembles a flickering lamp and is sometimes said to recede if approached. Much folklore surrounds the phenomenon. It was once was common throughout northern Europe. Although the learned would claim that the flames were caused by marsh gases, countryfolk knew better, and tales of mishaps made them weary.

In Wales, the flames were called 'corpse candles' and appeared just at the level of a raised human hand when a ghost walked invisible; they were thought to presage the death of those who saw them. Some say it is small winged fairies whose glowing lights can be seen at dusk in the meadows and grassy hills.

Germans said the lights were the ghosts of those who had stolen land. For Finns, such a light was a liekkiö, or 'flaming one,' and was believed to be the ghost of a child who had been buried in the forest.

In any case, the dancing flames were dangers to the living. Wayfarers who mistook them for the lights of a far-off shelter sometimes strayed into thickets where the ground grew shifty and sucked them down into the depths of bogs. Those who followed ghost lights, people said, were led to join the company of Death.

People in Northern Europe (in Sweden, Denmark, Finland, Estonia, Lithuania, Latvia and Ireland) thought the will-o'-the-wisp was marking out the location of a treasure which only could be taken when the light was visible. This was best achieved in the early autumn days, and for best result you should have a dead man's hand as well.