What does a Jack-o-Lantern symbolize?

"On Hallows' eve, the ancient Celts would place a skeleton on their window sill to represent the departed. Originating in Europe, these lanterns were first carved from a turnip or rutabaga. Believing that the head was the most powerful part of the body, containing the spirit and the knowledge, the Celts used the "head" of the vegetable to frighten off the embodiment of superstitions...The carving of pumpkins is associated with Halloween in North America[14] where pumpkins are both readily available and much larger- making them easier to carve than turnips. Many families that celebrate Halloween carve a pumpkin into a frightening or comical face and place it on their doorstep after dark."

-Wikipedia