A carved pumpkin whose top and stem have been cut out and interior removed, leaving a hollow shell that is then decorated to represent a face, illuminated from within by a candle. It is a symbol of Halloween.
A similar item made from a turnip
will-o'-the-wisp
How often have the words jack-o'-lantern and will-o'-the-wisp occurred in a corpus of books? (source: Google Ngram Viewer )