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.
Accounting period
The end of the fiscal year would move one day earlier on the calendar each year (two days in leap years) until it would otherwise reach the date four days before the end of the month (August 27 in this case). At that point the first Saturday in the following month (September 3 in this case) becomes the date closest to the end of August and it resets to that date and the fiscal year has 53 weeks instead of 52. In this example the fiscal years ending in 2011 and 2016 have 53 weeks.