In my mind a webapp is any website that has some complicated features and that's served from the web, but I know there are people who are a lot smarter than me here and they'll point out other features that I'm not noticing. For example:
- If it doesn't have a login system, can I still call it a webapp? (because most webapps end up being user-based).
- Should I think of a CMS as a webapp? and how about the sites that are built with it? probably they're not webapps, right?
- Is Gmail a webapp? I think so.
- Is twitter a webapp? Yes, though the functionality is rather simple.
So what conditions need to be met to call a website a webapp?
P.S. StackExchange's tag system defines web-applications as
applications that are accessed over the "web", which can mean the Internet, or an internal network (an intranet).