It is also the last day of meteorological winter in the Northern Hemisphere and the last day of meteorological summer in the Southern Hemisphere in leap years.
In the Gregorian calendar, the standard civil calendar used in most of the world, February 29 is added in each year that is an integer multiple of four, unless it is evenly divisible by 100 but not by 400.
The Julian calendar—since 1923 a liturgical calendar—has a February 29 every fourth year without exception.
[1] The convention of using February 29 was not widely accepted before the 15th century; from Julius Caesar's edict in 45 BC until the 16th century (formally), February 24 was doubled instead.
[2] In one of its attempts to adopt the Gregorian calendar, Sweden tried (unsuccessfully) to phase in the change by omitting leap days in the 11 successive leap-years, 1700–1740.