Leap year

A leap year (also known as an intercalary year or a bissextile year) is a year containing one additional day (or, in the case of lunisolar calendars, a month) added to keep the calendar year synchronized with the astronomical or seasonal year. Because seasons and astronomical events do not repeat in a whole number of days, calendars that have the same number of days in each year drift over time with respect to the event that the year is supposed to track. By inserting (also called intercalating) an additional day or month into the year, the drift can be corrected. A year that is not a leap year is called a common year.
For example, in the Gregorian calendar, each leap year has 366 days instead of the usual 365, by extending February to 29 days rather than the common 28. Similarly, in the lunisolar Hebrew calendar, Adar Aleph, a 13th lunar month, is added seven times every 19 years to the twelve lunar months in its common years to keep its calendar year from drifting through the seasons.

All the other months in the Julian calendar have 30 or 31 days, but February lost out to the ego of Roman Emperor Caesar Augustus.
Under his predecessor Julius Caesar, February had 30 days and the month named after him - July - had 31. August had only 29 days.
When Caesar Augustus became Emperor he added two days to 'his' month to make August the same as July.
So February lost out to August in the battle of the extra days.

The Roman calendar did have 355 days with an extra 22-day month every two years, until Julius Caesar became emperor and ordered his astronomer Sosigenes to devise a better system in the 1st Century.
Sosigenes decided on a 365-day year with an extra day every four years to incorportate the extra hours, and so February 29th was born.
As an earth year is not exactly 365.25 days long Pope Gregory XIII's astronomers decided to lose three days every 400 years when they introduced the Gregorian calendar in 1582. The maths has worked ever since but the system will need to be rethought in about 10,000 years' time.

Workers have realised that every leap year, they have to work one extra day for no extra pay.
If a person earns the national average salary of £26,500 a year, that works out at £2,208.33 per monthly payslip – which breaks down to £71.24 per day in a 31-day month but a daily wage of £78.87 in February.
This realisation prompted Karl Savage, who was a high school teacher from Maryland, to try and kick-start the “No Work on Leap Day Revolution” in 2008, when the extra day fell on a Friday.