There is indeed a leap day inserted every 4 years. But the actual rule is a bit more complicated. read more
For every year which ends in 00, even though it is a year divisible by four, it is actually not a leap year, with the exception that every 400 leap years it actually is a leap year. So, in any 400 year period, the number of leap days inserted is 97. read more
The name "leap year" probably comes from the fact that while a fixed date in the Gregorian calendar normally advances one day of the week from one year to the next, the day of the week in the 12 months following the leap day (from March 1 through February 28 of the following year) will advance two days due to the extra day (thus "leaping over" one of the days in the week). read more
Without Leap Day, we'd be out of sync by about six hours per year. Leap Day happens every four years unless that year is divisible by 100. If you were around in 1900, you would have missed out on the magic of February 29. Anyone born on Leap Day, will not get chance to celebrate their birthday every year. read more