Seasonal billing enables you to bill and entitle during a specific season and not at other times of the year. When a season set is attached to a billing plan, the billing will only occur during the seasons within that Season Set. Entitlements, by default, will also be for the season, although you can extend them before and after the season, or have them active continuously thoughout the year.
A Season Set is a list of seasons. This enables you to renew for the next season simply by adding another season to the set. For example, if you wanted to bill for the September-through-December football season on a monthly basis, you could create a billing plan with a season set containing the season (from September to December) of the current year. If you wanted to extend entitlements to include the pre-season and post-season, you could start the entitlements a month (or more) before the season begins, and extend them a month (or more) after the season. To extend billing and entitlements for subsequent years, simply add the next season/year to the set.