The DAA (Digital Analytics Association) changed their definition of a page some years ago to adapt the definition to the current situation.
The page that a user recognizes is no longer connected to the technical call of an html file from a web server.
E.g. in a Magento shop the entire purchase process is carried out on a single HTML page with several dynamic layers. Those layers open and close as need for the purchase.
The users really have the impression that they are served several pages not a single one. Hence the DAA (Digital Analytics Association) changed the definition of a page to something that can be adopted to the ‘look’ and ‘feel’ of a page: “An analyst definable unit of content.”
This definition has many advantages over the older one. One for example is that you can count the view of a PDF file as a page view, Ajax requests or even flash elements that just seem like a page to the user.
(Picture: gsagri04, http://openclipart.org)