February 29th only comes around once every four years, so it's a pretty special day for some people. Those would be the people who were born on February 29th, and only have a real birthday date four times by the time they get their driver's license. But there are traditions celebrated the world over for this rare date. The most common is that February 29 is the one day that women can propose marriage to men.
Where did the tradition begin? Supposedly Ireland in the 5th century. Saint Brigid of Kildare, arguing that women were languishing away waiting for their shy beaux to pluck up the nerve to pop the question, asked Saint Patrick to give a day they might do the deed themselves. A little haggling was involved, with Saint Patrick first suggesting every seven years, but eventually the Leap Year was settled on. According to folklore, Saint Brigid then immediately proposed marriage to the Irish saint.
As the Irish nun would have been around nine or ten years old when St. Patrick died in 461 A.D, this story is a little dubious, but no less charming for it.
Yes, it's an outdated concept, but there are specific traditions centered around the idea, including fines levied against men who turned down such a proposal in various European countries. Read about those traditions, plus what they eat in Taiwan, what they drink in London, and what they publish in France on February 29, at Buzzfeed.