People often have a hard time getting the terminology right. 16 billion visitors is synonymous with 16 billion uniques, so not possible - by quite some way.
If you load the site, then click a few links (say 4 pages in total), then close your tab/window, then load the site and click a few more links (another 4 pages) then you are 1 visitor, 2 visits, 8 pageviews.
From the wording I would imagine they mean visits, but from that number pageviews seems easier to believe.
Related: I blame Google Analytics for much of the confusion, as they are one of the few places (at least that I've come across) that refer to unique users as "visitors", and I've found that trips up many people when compared with "visits".
If you load the site, then click a few links (say 4 pages in total), then close your tab/window, then load the site and click a few more links (another 4 pages) then you are 1 visitor, 2 visits, 8 pageviews.
From the wording I would imagine they mean visits, but from that number pageviews seems easier to believe.
Related: I blame Google Analytics for much of the confusion, as they are one of the few places (at least that I've come across) that refer to unique users as "visitors", and I've found that trips up many people when compared with "visits".