A page group is a collection of related pages. Every page belongs to a page group. A page group also contains any supporting objects required for the pages within it, for example styles, page templates, categories, and perspectives.
The purpose of a page group is to group related pages together, and to allow you to provide a structure for those pages. You can also set properties at the page group level that apply to all the pages within that page group. For example, you can specify a default style or page template to use for all pages in the page group, and the type of content that contributors can add to pages in the page group. For more information, see Editing page group properties.
Creating a page group
What is a page group administrator?
Page group privileges