A regular, non-leap year has 365 days. This is the case for the majority of years in the calendar. However, to keep the calendar year synchronized with the astronomical year, which is approximately 365.2422 days long, a leap year is introduced every four years.
In a leap year, an extra day is added to the calendar, making it 366 days in total. The additional day is added to the month of February, making it 29 days instead of the usual 28. So, on average, a year is approximately 365.25 days long when accounting for leap years