This year is a leap year. Which means that the month of February will have an extra day on the 29th.
Generally, a leap year occurs in a year evenly divisible by 4, example is in 2008 and this year, 2012. But there is an exception for this rule. An exception is if the year is evenly divisible by 100, unless it is evenly divisible by 400. So the years 2100, 2200 and 2300 are not leap years but the year 2400 is a leap year.
Source: http://en.wikipedia.org/wiki/Leap_year
