Leap Year (Leap Year) was created to make up for the difference between the number of days in the year and the actual period of the Earth's revolution due to artificial calendar rules. The year in which the time difference is filled is a leap year. In leap years, there are 366 days (31, 29, 31, 30, 31, 30, 31, 30, 31, 31, 31, 31, 31, 31, 31, 31, 30, 31, respectively).