February 2012: A Leap Year
2012 is a special year because it is a leap year. It has 366 days instead of 365 days.
Why do you think leap years form every 4 years?
Leap Years are needed to keep our calendar in alignment with the Earth's revolutions around the sun. It takes the Earth approximately 365.242199 days to circle once around the Sun. This equals to 365 days plus an extra 6 hours.
We follow the Gregorian calendar which has only 365 days in a year. If we didn't add a day on February nearly every 4 years, we would lose almost six hours off our calendar every year. After only 100 years, our calendar would be off by approximately 24 days!!
There is a division of 4 years between each leap year because the 6 hours extra in each year need 4 years to make an extra day. This extra day is given to the 4th year. The last leap year was 2008. There was 6 hours period in 2008, 2009, 2010 and 2011 to make the extra day in 2012. The extra 6 hours over the next four years will provide a extra day in 2016.
In Gregorian Calendar, a leap year needs to be evenly divisible by 4 and if the year is an end of a century year then it has to be divisible by 400. The leap year extra day is given to February because February has two less days during the regular year.
Julius Caesar introduced Leap Years in the Roman empire over 2000 years.
[Editor: A small correction to Adithya's article. It is the 6 extra hours in 2009, 2010, 2011 and 2012 which are adjusted by an extra day in 2012. The concept of why we have leap year is correctly explained by Adithya.]