Date or <a class="localLink" href=https://schema.org/"/DateTime">DateTime during which a scheduled <a class="localLink" href=https://schema.org/"/Event">Event will not take place. The property allows exceptions to a <a class="localLink" href=https://schema.org/"/Schedule">Schedule to be specified. If an exception is specified as a <a class="localLink" href=https://schema.org/"/DateTime">DateTime then only the event that would have started at that specific date and time should be excluded from the schedule. If an exception is specified as a <a class="localLink" href=https://schema.org/"/Date">Date then any event that is scheduled for that 24 hour period should be excluded from the schedule. This allows a whole day to be excluded from the schedule without having to itemise every scheduled event." />
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exceptDate

A Schema.org Property

This term is in the "new" area - implementation feedback and adoption from applications and websites can help improve our definitions.
Thing > Property :: exceptDate
Defines a Date or DateTime during which a scheduled Event will not take place. The property allows exceptions to a Schedule to be specified. If an exception is specified as a DateTime then only the event that would have started at that specific date and time should be excluded from the schedule. If an exception is specified as a Date then any event that is scheduled for that 24 hour period should be excluded from the schedule. This allows a whole day to be excluded from the schedule without having to itemise every scheduled event.

Values expected to be one of these types

Used on these types

Source

https://github.com/schemaorg/schemaorg/issues/1457