I just used the Quality Check plugin to search my library for the term "page-list" and it found a few books that have it. It's actually in the nav file of the book and is under:
Code:
<nav epub:type="page-list">
I don't know if that's created by Calibre's conversion routines or if the author created it and it came over directly during the conversion. I assume that would be used as a means of jumping directly to a location that corresponded to a specific page of the specific edition of a source book (most probably a printed book).