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".
In traditional stories it invariably appears in proximity to marshes, swamps, or other wetlands. A person traveling alone at night sees the will-o'-the-wisp at a distance and mistakes it for a light source held by a person. Attempting to approach it causes it to recede, creating the illusion that the flame is leading the traveler to safety. The traveler follows the flame off the road, deep into the swamp, at which point the will-o'-the-wisp abruptly vanishes, leaving the traveler in complete darkness, far off the road and lost in a swamp.
It is believed that the myth has at least some basis in reality: dead vegetation decaying in a swamp environment emits a number of flammable gasses, including ones that ignite spontaneously when exposed to oxygen.
