The oddity of February 29th had arrived again; as it only shows up every 4 years. Ever wonder what's the reason behind that? I have.. and finally decided to do some research for myself today. Here's the deal... apparently, the solar/tropical year is approximately 365.2422 days long. Obviously for simplistic reasons, the human calendar cannot be comprised to match that number exactly. The concept of a 'leap year', February 29th, is to make up for the time of those numbers you see above after the decimal.
Humans usually ignore excessive numbers after the decimal (i.e. the actual cost of your fuel, weight of something, averages when doing a math equation etc.) to keep things less complicated, I suppose. Interestingly found, you can't ignore Mother Nature's natural year length ... as evidence in history shows a result of wildly shifting dates and confusion (agriculturally, religiously, holidays etc.) This extra day to accommodate the 'lost' time helps to stay in tune with the seasons.
You can read up on more about the Leap Year and various calendars at National Geographic.