Leap year
The name "leap year" probably 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 Day (December 25) fell on a Sunday in 2016, and Monday in 2017, then it fell on Tuesday in 2018, and will fall on Wednesday in 2019 but then "leaps" over Thursday to fall on a Friday in 2020.
Hanke–Henry Permanent Calendar
The key difference between Robert McClenon's calendar proposal and Henry's modification is that the former has a simple rule for determining which years have a leap week. This rule resembles the Gregorian leap year rule and has the same cycle length. Years whose numbers are divisible by 5 have a leap week, but years whose numbers are divisible by 40 do not have a leap week unless also divisible by 400. The main drawback of this rule is that the new year varies 17 days relative to the Gregorian new year (e.g. year 1965 begins 11 days earlier than Gregorian 1965 and year 2036 begins 6 days later than Gregorian 2036), whereas Henry's rule ensures that the new year always begins within three days of the Gregorian new year.