Updated Feb 29, 2012
ONE OF the convenient fictions we live by holds that there are exactly 365 days in a year. In point of fact, the earth turns roughly 365 and a quarter times on its axis by the time it has completed a full year's orbit around the sun, which means that periodically the calendar has to catch up, thus the convention of leap years. A leap year contains one extra day, February 29, for a total of 366 days. 2012 is a leap year.
So, where does the "leap" come in? This is a perennial source of confusion. In a normal sequence of years, a calendar date that falls on, say, a Monday one year will fall on Tuesday the next, Wednesday the year after that, Thursday the year after that, and so on. But every fourth year, thanks to the extra day in February, we "leap" over the expected day of the week Friday, in this case and that same calendar date lands on Saturday instead.
Even more abstruse is the arithmetical formula used to calculate which years are leap years, here described as succinctly as one could ever hope by Rev. E. Cobham Brewer, author of Brewer's Dictionary of Phrase and Fable:
[A leap year is] any year whose date is exactly divisible by 4 except those which are divisible by 100 but not 400.
Why such complexity? Because the exact number of days in a solar year is actually ever-so-slightly less than 365.25 (it is 365.242374, to be precise), so the algorithm had to be designed such that every now and then a leap year is skipped to keep the calendar on track over the long haul.
Leap year / leap day folklore
Persons born on leap day, February 29, are called "leaplings" or "leapers." However fun it may be to rib them for enjoying 75 percent fewer birthdays than the rest of us, they do have the special privilege, between leap years, of celebrating their nativity a full day earlier than scheduled if they so choose. It was once thought that leapling babies would inevitably prove sickly and "hard to raise," though no one remembers why.
Ironically, notwithstanding the fact that the whole point of adding an extra day to February every four years was to align the human measurement of time more closely with nature, in days gone by folks apparently believed that monkeying with the calendar that way might actually throw nature out of whack, and even hamper the raising of crops and livestock. It used to be said, for example, that beans and peas planted during a leap year "grow the wrong way" whatever that means and, in the memorable words of the Scots, "Leap year was never a good sheep year."
The tradition of "ladies' privilege"
In keeping with the theme of nature gone awry, a whimsical tradition dating back at least four centuries (and still trotted out at four-year intervals by newspaper feature writers) holds that leap years confer upon women the "privilege" of proposing marriage to men instead of the other way around. The convention was (in literature, if not in reality) that any man who refused such a proposal owed his spurned suitor a silk gown and a kiss provided she was wearing a red petticoat at the moment she popped the question.
The origin of this romantic tradition is long forgotten and steeped in legend. One tidbit often repeated in 19th-century sources claimed it grew out of a statute passed by Scottish Parliament in 1288, of which one of the many quoted versions reads:
It is statut and ordainit that during the reine of hir maist blissit Magestie, ilk maiden ladye of baith highe and lowe estair shale hae libertie to bespeak ye man she likes; albiet, gif he refuses to tak her till be his wif, he sall be mulcit in ye sume of ane hundredth poundis or less, as is estait mai be, except and alwais gif he can mak it appear that he is betrothit to ane other woman, then he shall be free.
Mind you, this passage was already considered suspect by some of the same Victorian authors who quoted it not only because the text couldn't be sourced ("the only authority for this statement is the 'Illustrated Almanac' for 1853," wrote one critic, "which probably manufactured the statute as a jest") but also because its "old English" phraseology rings too modern for the year 1288. In addition, the text itself proved to be quite variable with regard to grammar, spelling, and even content, with some versions boasting an extra clause specifying that the law pertained to "ilk yeare knowne as lepe yeare."