Document-centric, form-driven websites aren’t traditionally called apps. The Wikipedia website isn’t an app. Web forums aren’t apps. “App” implies that essential parts of the interaction logic are driven by client-side code (JS, not HTML) that couldn’t similarly be implemented by HTML forms.

Sure Wikipedia is an app, long as you think of static websites as a subset of web apps. One might say that makes the term meaningless, I say it's a deliberately vague term because people don't want or need to get cornered by fine distinctions. Otherwise it's endless quibbling over whether things like search do or do not count toward a site being a "real" app.