I have a slightly different question - many of the answers in here make it sound like creating and deploying a new web app is practically a twice-a-week kind of thing for quite a few folks. What kinds of things are people so frequently creating and putting up in a hurry?

A large portion of the apps are intranet thing, instead of Internet. Business apps that are used in house.

Plus almost all websites are a kind of web app. And these have a complex backend for managing the content. While we browse the front end.

I think you are underestimating what is a web app. Think about any website that requires a password - that is a web app because presumably it will do some personalization. Any content serving site is at least backed by a content management system which is a web app.

To me, "web application" is a front-end application that runs on the user's computer in a web browser. Having a back end that runs code doesn't qualify in my mind. Otherwise, basically any website qualifies as a web app, including one written in pure HTML, which doesn't make sense to me.