February 29, known as a leap day in the Gregorian calendar, is a date that occurs in most years that are evenly divisible by 4, such as 2004, 2008, 2012 and 2016. Years that are evenly divisible by 100 do not contain a leap day, with the exception of years that are evenly divisible by 400, which do contain a leap day; thus 1900 did not contain a leap day while 2000 did. Years containing a leap day are called leap years. February 29 is the 60th day of the Gregorian calendar in such a year, with 306 days remaining until the end of that year.
From the Groundspeak newsletter on the 24th Feb 2012:
Leap Day Geocaching
There's one thing money cannot buy and all geocachers want - more time to go geocaching. On Leap Day (this February 29), geocachers' wishes come true; there's a whole extra day on the calendar to go geocaching! And Geocaching.com is providing an additional incentive to get outside on the 29th - a Leap Day souvenir for all accounts logging a "Found it" or "Attended" that day. You'll receive the colorful Leap Day Souvenir on your Geocaching.com profile.
You'll also help in a record-breaking attempt. Last Leap Day, way back in 2008, some 36,696 distinct accounts logged an "Attended" or "Found it" on a cache. We're aiming to double that number this year with at least 73,392 distinct accounts logging a cache on February 29. In order to count toward the goal, people only have to log a single cache.
More than 900 Event Caches are already planned for Leap Day. If the 25,000 adventurers expected to attend these events log their attendance on the 29th, we'll be more than 30% of the way toward our goal. But we still need your help in order to reach 73,392! So talk to your fellow geocachers, your friends, and your co-workers; tell them about going geocaching (and logging their find) on February 29. We will be reporting our progress toward the goal on the Latitude 47 blog and the Geocaching.com Facebook page.
As an extra bonus, Premium Members who love to look at their "finds by date" statistics have a rare opportunity to fill in the February 29 square - the 366th day of geocaching!