Leap Year

A leap year is a year containing one additional day. A year that is not a leap year is called a common year.

The name "leap year" comes from the fact that while a fixed date in the Gregorian calendar normally advances one day of the week from one year to the next, the day of the week in the 12 months following the leap day (from March 1 through February 28 of the following year) will advance two days due to the extra day (thus "leaping over" one of the days in the week). For example, Christmas fell on Tuesday in 2001, Wednesday in 2002, and Thursday in 2003 but then "leapt" over Friday to fall on a Saturday in 2004.

Leap Day February 29 is a date that usually occurs every four years, and is called leap day. This day is added to the calendar in leap years as a corrective measure, because the Earth does not orbit the sun in precisely 365 days.