what is leap day and 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.
February 29, also known as the leap day of the Gregorian calendar, is a date that occurs in most years that are divisible by 4, such as 2004, 2008, 2012, 2016 and 2020. Years that are divisible by 100, but not by 400, do not contain a leap day.