Happy Leap Day!
Every four years, we get an extra day at the end of February in order to synchronize the calendar with the solar year. You can find more information here.
If you're wondering how to spend your extra 24 hours a day, NPR has an hour-by-hour list of suggestions, including bury a time capsule.
Some people also consider Feb. 29 to be Sadie Hawkins Day -- when women ask men out -- and in the early 20th century, it was common knowledge that women could propose to men during leap years.
Slate has an amusing slideshow of postcards encouraging women to get their man before the year was out. This one's my favorite.
Women don't have to wait until a leap year to pop the question anymore, but I don't know women proposing to men is considered the norm yet. In popular books and movies, the guy is still usually the one who asks the question. Ditto for every jewelry ad I've ever seen. But if you are a woman thinking about proposing on a leap year, Wikihow offers an 11-step guide.