Leap year is basically a year with an extra day in it, February 29, and occurs once every four years. The reason for this is to keep the seasons, astronomical events and time differences in sync. This has to do with the Gregorian calendar, which is used almost everywhere in the world. Leap Year is directly related to the Earth and how many times it orbits the sun in one year. There are not actually 365 days in a year, but 365 1/4 days in a year. So basically, four quarters would make up an extra day, hence adding a day every four years.