'Leap Day' is February 29, which is an extra (intercalary) day added during a Leap Year, making the year 366 days long – and not 365 days, like a common (normal) year. Nearly every 4 years is a Leap Year in our modern Gregorian Calendar.
Ever since Leap Years were first introduced over 2000 years ago with the transition from the Roman Calendar to the Julian Calendar in 45 BCE (Before Common Era), Leap Day has been associated with age-old Leap Day traditions and folklore.
According to an old Irish legend, or possibly history (it's hard to tell with the Irish), St Bridget struck a deal with St Patrick to allow women to propose to men – and not just the other way around – every 4 years. This is believed to have been introduced to balance the traditional roles of men and women in a similar way to how Leap Day balances the calendar.
In some places, Leap Day has been known as “Bachelors’ Day” for the same reason. A man was expected to pay a penalty, such as a gown or money, if he refused a marriage proposal from a woman on Leap Day. In many European countries, especially in the upper classes of society, tradition dictates that any man who refuses a woman's proposal on February 29 has to buy her 12 pairs of gloves. The intention is that the woman can wear the gloves to hide the embarrassment of not having an engagement ring. During the middle ages there were laws governing this tradition.
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