leap year
A leap year is equal to 366 days.
There is an extra day in a leap year compared with a normal year. There are 366 days in a leap year, rather than 365 days.
29 February is always the extra day, and it is added every four years. A day is added because the Earth takes 365.25 days, or 365 days and a quarter, to orbit the Sun once.
A leap year happens every four years. Each leap year is a multiple of 4. Therefore, 2012 was a leap year. 2020, 2024 and so on, will also be leap years.