"This website has many webpages."
Translation:Ĉi tiu retejo havas multajn retpaĝojn.
Oops, I just discovered that I was wrong! I asked around and people seem not to make the distinction. I explained that every time you click the Next button on a site the site takes you to a new page, and they immediately understood.
As a web developer I know though that every file (html, php, whatever) on the server that's served to the browser constitutes another page on the website/domain, even if the page is compiled from information on a database and served to the browser. Before tabbed browsing we used to have the option to refresh the page, nowadays you can refresh the tab.
Also see the Grammarist.
I doubt it. The distinction can be forced when one talks about pages on a website, but webpage and website are pretty blurred. Plus if you mix in multipage pages (all the top 10 lists) and single page applications (like Duolingo) it's hard for a layperson to even tell the difference (and you get lost in technical details on the other end of the matter).
So if you insist, there's is the distinction consultjohan described, but unless someone puts those two terms in the same sentence (or it's pedant quizzing you), it's safe to consider them as a synonyms.