That's the catchword, the first word of the next page. It helps with keeping the pages in the correct order when binding the book. It could also be an aid when reading aloud, to give the reader one word of "buffer" when turning the page.

That's a preview of the first word of the next page. I guess it helps to switch between pages more smoothly.

I would guess it is to aid a speaker reading aloud so as not to have an awkward pause between pages.