The Month Days settings are used in the Advanced Recurring Options for monthly and yearly events to specify which days of the month events should occur on. By default, only the day of month of the event start date is selected for both monthly and yearly events. The event can be made to occur on additional month days by selecting those days.
The Show All and Show None buttons can be used to quickly toggle all months days on and off.
See Also: Examples, Advanced Monthly Options, Advanced Yearly Options