A liekkö is in Finnish folklore, an Ignis Fatuus light, comparable to the British Jack-O'-Lantern. The liekkö, which means “the flaming one,” is believed to be the soul of a child who was buried in the forest. It presides over plants, roots and trees.
SOURCE:
The Encyclopedia of Ghosts and Spirits – Written by Rosemary Ellen Guiley – September 1, 2007