What are quotations called in a book when they serve to introduce the story?
For example, many writers will select a quotation or two, possibly even a poem or song excerpt, before beginning a major part of their novel as a quasi introduction thereto, as a way of opening the story’s theme in capsulized form.
What is the proper name for this process, or for these selected quotations?
They’re called epigraphs.
They’re called epigraphs. An epigraph is a quotation that is placed at the start of a work or section that expresses in some succinct way an aspect or theme of what is to follow.