Since the early days of the web, the 'Page' as we know it as evolved. This concept, better called Impression, has referred to 'what is shown to the user'.
With the web, the realization of Impression has also evolved. In the days of Web 1.0, the Impression was a Page. Since then, companies have reached out to impress users in a variety of different users, through advertising, widgets on various portal web sites, as applications on the iPhone or on the Nintendo Wii.
An Impression then becomes the information that the user consumes through the various organs of sense - seeing, hearing, smelling, tasting, or touching. Of course many of these forms are yet to be realized for mainstream adoption on the Internet.
To focus on the web page of today, it is best characterized as being composed of content modules. It then is a Composite Page, which comprises the Page, Layout, Placement and Module. The Module is a piece of content that is of the smallest granularity of interest to analytics. Placement is where the Module shows up, and is a rectangular piece of 'real estate' in the browser. Layout is how the various Placements are 'laid out'. And the Page itself is the overall construct that appears in the web browser.
To summarize, the Page is then really a Composite Page, which constitutes an Impression in the web browser.
