Leap year
The term leap year probably comes from the fact that a fixed date in the Gregorian calendar normally advances one day of the week from one year to the next, but 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 day in the week. For example, Christmas Day (December 25) fell on a Tuesday in 2012, Wednesday in 2013, Thursday in 2014, and Friday in 2015, but then leapt over Saturday to fall on a Sunday in 2016.
Leap year-3