A leap year is a year with 366 days
A normal year has 365 days, but if there is a leap day in that year, then the year has 366 days. Since the beginning of our era, there have been 488 leap years. It assumes a calculation that has started since 1582: each year that is divisible by 4 is a leap year (with the exception of century years). The time the Earth needs to run in its spell to turn the sun from Spring point to spring point is not exactly 365 days. If we did not correct this we would be celebrating old and new too early, or the fact that the seasons are going to start on other days. Therefore, every four years and the day there is extra to correct as much as possible.
Why do we have a leap year?