They're called Breadcrumbs because they're reminiscent of the trail of crumbs Hansel
dropped in the woods so he and Gretel could End their way back home.
Unlike "You are here" indicators, which show you where you are in the context of the site's
hierarchy, Breadcrumbs only show you the path from the Home page to where you are.
(One shows you where you are in the overall scheme of things, the other shows you how to
get there—kind of like the difference between looking at a road map and looking at a set of
turn-by-turn directions. The directions can be very useful, but you can learn more from the
map.)
You could argue that bookmarks are more like the fairy tale breadcrumbs, since we drop
them as we wander, in anticipation of possibly wanting to retrace our steps someday. Or
you could say that visited links (links that have changed color to show that you've clicked
on them) are more like breadcrumbs since they mark the paths we've taken, and if we don't
revisit them soon enough, our browser (like the birds) will swallow them up.