Most of us have been taught that it takes the earth 365 days to make one revolution around the sun, but that's not quite correct. Actually, it takes the earth approximately 365.25 days (give or take a few minutes) to circle around the sun. So, once every four years, we add an extra day back to the calendar to compensate. If we didn't, eventually, our calendars would be significantly "off" in regard to the seasons (granted - it would take a long time, but it would happen).
So why add the day to February instead of adding it to any other month? Well, we follow the Gregorian Calendar, and the Gregorian Calendar is designed in such a way as to keep the vernal equinox as close as possible to March 21st (which has to do with what day Easter falls on...). So adding the day to February works to keep the vernal equinox where we (us Gregorian Calendar followers) like it.
So - in celebration of gaining a day, and the cognitive "leap" it requires just to understand it, enjoy a refreshing Leap Frog Cocktail with a friend.
The Leap Frog
1 1/2 measures gin
1/2 measure freshly squeezed lemon juice
Ginger Ale
Mix gin and lemon juice with cracked ice in a highball glass and top fill with cold ginger ale. Add a cocktail cherry if desired.