A Wiki Page is simply the basic building block of a Wiki Wiki Web that contains text and images. See WikiStructures and WikiWikiWeb for more information.
Wiki pages can have an edit template to predefine initial content, see Templates
Wiki pages are stored in individual flat files, see File Format? and File Advantages.
This page may have a more recent version on pmwiki.org: PmWiki:WikiPage, and a talk page: PmWiki:WikiPage-Talk.