NOTE: Tracker Reports have been deprecated/and removed in tracker 9 for the feature "Reports", which now contains the same functionality and more for trackers and now tiki logs... More to come later.
Tracker reports is a system that is really in an alpha state right now, and will still evolve much as time goes on. As it sits right now it uses an item id of the related tracker and allows you to create reports that join trackers together. If anyone wants to take it for a test drive, let me know what your findings are, the file it tiki-tracker_reports.php. Right now it outputs a url that is to be used with tiki-tracker_export_join.php, but we eventually plan on saving the url so that you can have a dynamic "view" of a tracker.