Fourteenth means the item that comes right after the thirteenth in a sequence. If you're standing in line and there are thirteen people ahead of you, you're in the fourteenth position. February 14th (often written as February fourteenth) is the fourteenth day of the second month.

The word shows up often in history and formal titles. King Louis XIV of France was called “Louis the Fourteenth” because thirteen other French kings named Louis had ruled before him. The Fourteenth Amendment to the United States Constitution, adopted after the Civil War, guaranteed citizenship and equal protection under the law to all people born in the United States.

When you write the number 14th, you're using the shortened form of fourteenth. The “th” ending tells you it's describing position in a sequence, just like fifth, eighth, or twentieth. If someone says “I finished in fourteenth place,” they're telling you that thirteen other people finished ahead of them.