leap year

The calendar is approximately a quarter of a day short, which is why we have leap years, to bring the calendar back in line with the Earth's orbit.

Like clockwork, leap years roll around every four years.

She was born on 29 February, an elusive day that appears once every four years in a leap year - so she's only had seven birthdays on her actual day in her lifetime.

The extra accrued time results in Feb. 29 appearing on the calendar every fourth year — leap year — to help the seasons line up.

For centuries, attempts to sync calendars with the length of the natural year have sowed chaos—until the concept of leap year provided a way to make up for lost time.