A leap year is a year that contains an extra day, making it 366 days long instead of the usual 365. This additional day is added to the month of February, which then has 29 days instead of the typical 28. Leap years occur approximately every four years to help synchronize the calendar year with the Earth's orbit around the Sun.

The reason for this adjustment lies in the fact that the Earth takes about 365.2422 days to complete one orbit around the Sun, known as a tropical year. Simply using a 365-day calendar would gradually cause the seasons to drift, as the calendar year would not match up with the solar year. By adding an extra day every four years, the calendar stays more aligned with the Earth's revolutions.

However, there is a slight exception to this rule. A year that is divisible by 100 is not a leap year unless it is also divisible by 400. For example, the year 1900 was not a leap year, but the year 2000 was. This system helps to further refine the alignment between the calendar and the solar year.

Leap years have been part of the Gregorian calendar since its introduction in 1582. They play a significant role in various cultures and traditions, often symbolizing change or renewal. Understanding leap years is essential for accurate timekeeping and planning events that depend on precise dates.

In summary, a leap year is a method of adjusting our calendar to account for the Earth's slightly longer orbit around the Sun. By adding an extra day every four years (with some exceptions), we ensure that our calendars remain synchronized with the natural cycles of the planet.