It takes the earth one day to complete one spin on its axis. The time it takes the earth to complete one trip around the sun is one year.
But these units of time don’t divide evenly, resulting in our calendar year being 365 days, 5 hours, 48 minutes and a little over 45 seconds long. Every 4 years we take those extra hours and minutes and fit it in an extra day, on February 29th, which we call Leap Day. Every fourth year thus is Leap Year. If we did not have the extra day every 4 years, in 100 years our calendar would be off by 24 days.
2012 was a Leap Year. As was 2008 and 2004 and the year 2000. Normally, a year that can be evenly divided by 100 is not a Leap Year but if it is divisible by 400 then it is. Thus the year 2000 was a Leap Year but the year 1000 was not and neither would be the year 3000.
The Chinese calendar has a leap month about every 3 years and the name of the leap month is the same as the previous lunar month. The Jewish calendar has a leap year 7 times in a 19-year cycle.
The chance of being born on Leap Day in the Gregorian calendar is about 680 out of a million (1 in 1470). Which means little more than 4 million people (out of a world population of 7 billion) have their birthdays on Leap Day whereas on average approximately 19 million people share a birthday every day other than Leap Day.
Ladies, if he did not pop the big question on Valentine’s Day then February 29th is your day because tradition has it that a woman can propose to a man on Leap Day.