How many days are in a leap year?

A leap year contains 366 days, which is one day more than the standard 365 days in a common year. This additional day occurs on February 29th, which is added to the calendar every four years to help synchronize the calendar year with the solar year. This adjustment accounts for the fact that a complete orbit of the Earth around the Sun takes approximately 365.25 days.

The leap year system is designed to ensure that calendar dates remain consistent with the seasons over time. Therefore, the correct answer reflects this understanding of leap years in relation to the annual calendar.