Standards: Leap Year
Leap years are years with 366 days instead of the usual 365. They are necessary because a year is actually 365.242 days long, not 365 days as commonly stated. Leap years occur every four years on those evenly divisible by four, except those which are both divisible by 100 and not divisible by 400. The extra day is added to the calendar as the 29th of February.
2012 is a leap year.