What is a leap year?

Hint- This kind of year is the one which occurs once in every four years. This year consists of an intercalary day that falls in the month of February.

Complete answer:
A leap year which is also known as an intercalary year or bissextile year refers to a calendar year which specifically consists of an additional day. While in the case of a lunisolar calendar, a month is added in order to keep the calendar year synchronized along with the astronomical year or seasonal year. Since the astronomical events as well as seasons do not repeat in a whole number of days, calendars which have the same number of days in each year drift over time with respect to the event that the year should track.
Through inserting (that is known as intercalating in technical terminology) an additional day or month into the year, the drift can be corrected. A year that is not a leap year is said to be a common year. Leap years refer to those years where an extra, or intercalary, day is added to the end of the shortest month, that is February. The intercalary day is February 29 that is commonly said to be a leap day. Leap years consist of 366 days instead of the usual count of 365 days and occur almost every four years.

Note:
The regular calendar in total has 365 days in a year, because that's normally how long it takes for the Earth to orbit the Sun. While, a leap year occurs in every year which is divisible by four, but only in century years that are evenly divided by 400.