Real Dictionary

leap year
countable noun: A leap year is a year which has 366 days. The extra day is the 29th February. There is a leap year every four years.

leap year in American English
a year of 366 days in the Gregorian calendar, occurring every fourth year: the additional day, Feb. 29, makes up for the time lost annually when the approximate 3651⁄4-day cycle is computed as 365 days: a leap year is a year whose number is exactly divisi
noun: a year that contains 366 days, with February 29 as an additional day: occurring in years whose last two digits are evenly divisible by four, except for centenary years not divisible by 400

leap year in British English
noun: a calendar year of 366 days, February 29 ( leap day) being the additional day, that occurs every four years (those whose number is divisible by four) except for century years whose number is not divisible by 400. It offsets the difference between the leng