It refers to a mysterious light seen at night, often in marshlands or cemeteries, that is believed to be a supernatural phenomenon.
Here's a breakdown:
* Le: The French definite article, meaning "the."
* Feu: French for "fire."
* Follet: A French word referring to a mischievous spirit, often associated with fire or light.
So, literally, "le feu follet" translates to "the fire spirit" or "the fire goblin." But in English, we use the more poetic term "will-o'-the-wisp."