A Page Set (or Page Sequence) is a sequence of multiple Page Layouts that apply when the page's number meets certain conditions (is first, is last, or when a condition from the XML is met). Your template may end up being composed of many page sets, and this can be very useful because you may want to assign different layouts to change design properties such as orientation, page size, and much more specifically for that range of pages. Additionally, you can choose to conditionally display an entire page set based upon your data source or specify to create a page for a set of repeating content in your data.
You can learn more about the design and usage of Layouts and Page Sets by visiting our help section on Pagination.
Figure 1: The Pagination Pane offers easy access to configuring a Page Set.