According to History.com, commonly referred to as The History Channel, people have been making Jack O'Lanterns for centuries. The custom originates from an Irish myth about a a man named "Stingy Jack." Back in the day, the carved out turnips, potatoes, or beets (that's what they used in the old country) were referred to as "Jack of the Lantern." Then it was shortened to Jack O'Lantern.
An apostrophe is used in the contraction O'Lantern.
Apostrophes are best known for indicating possession. Maybe that is why they get so mucked up in contractions.
Often, the open single quotation mark is used in place of the apostrophe. Here's a good example:
See the difference?
English Grammar for Dummies rules that in English you can use contractions to shorten a word by removing one letter or more and substituting an apostrophe in the same spot. For example, chop wiout ofI will,throw in an apostrophe, and you haveI’ll. The resulting word is shorter and faster to say, with only one syllable (sound) instead of two.
Apostrophes are not without a sense of humor. Check out Apostrophe Catastrophe. Soon you'll be submitting your own examples.