"February 29, also known as leap day or leap year day in the Gregorian calendar, is a date that occurs in most years that are divisible by 4, such as 2008, 2012, 2016, 2020, and 2024. Years that are divisible by 100, but not by 400, do not contain a leap day. Thus, 1700, 1800, and 1900 did not contain a leap day, 2100, 2200, and 2300 will not contain a leap day, while 1600 and 2000 did, and 2400 will. Years containing a leap day are called leap years. February 29 is the 60th day of the Gregorian calendar in such a year, with 306 days remaining until the end of the year. In theChinese calendar, this day will only occur in years of the monkey, dragon, and rat.
A leap day is observed because a complete revolution around the Sun takes slightly longer than 365 days. It compensates for this lag, realigning the calendar with the Earth's position in the Solar System; otherwise, seasons would occur in a different time than intended in the calendar year."