Range of Dates holidays are defined as having a start and end date.
Typically, this type of holiday refers to an event (trade fair, olympics, company event, convention, ...) rather than to a holiday per se. This type of holiday rule is similar to Arbitrary Dates rules in that it cannot easily (or at all) be predicted or calculated, but Range of Dates rules add an element of duration.
Note that you can choose to exclude some weekdays from the range of dates (for example, excluding the weekend days from a 2 week company event).
See also: Recurrence Rules Options.