- websites as-you-know-them, which goal is to provide _information_
- webapps, which goal is to provide _services_
But the second kind is completely different. When you (as in the general you) are using GMail, you actually want to use an application to manage your mail, possibly send and receive them. Whether it's in your chrome browser or native in your OS matters only as far as how easy it is to install, and on that point the web has won. But it's just a happy accident of how things have evolved.
I guess some things are really "documents" (Wikipedia articles) and some things are really "apps" (HTML5 games), but it seems like there's a huge swath of uncritical groupthink that's saying you're web thing needs to be an "app" because iPhone.