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").
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.