February 29th comes around just every four years (most of the time), putting events and births on that date into a sort of existential limbo.
Why does a leap year exist? Because Earth's orbit around the sun doesn't perfectly line up with the modern human (Gregorian) calendar -- an Earth year is 365 days and 6 hours (minus about 11 minutes -- it's 365 days, 5 hours, 48 minutes and 45 seconds, to be more precise). Every four years we add a 24-hour day (Feb. 29) to catch up with Earth's orbit.
Leap days are added in years divisible by 4. Unless it's a leap year divisible by 100, but NOT divisible by 400. Simple, right? So, three leap years are removed every 400 years. That's to account for that 11 minutes mentioned above.
But what's the legal status of people born on Feb. 29 -- a day that only comes once every four years? Depends where you live. For instance in Britain, Feb. 29th birthdays in leap years are legally on March 1. In New Zealand, it's Feb. 28. This is important when reaching legal drinking age, getting a driver's license and other legal hurdles of note.
How many living people were born on Feb. 29? There are an estimated 187,000 Americans and 4 million Earthlings born in a leap year.
What does it mean to be born in a leap year? At the very least, you are a member of a very elite group: The Leaplings.
Pope Paul III: The Pope (from 1534-1549)
Superman: A leapling in comics from the 1960s to the 1980s