Do we have a good definition for "web application"?
Here's the definition for Application software from Wikipedia
Application software, also known as an application, is computer software designed to help the user to perform singular or multiple related specific tasks. Examples include enterprise software, accounting software, office suites, graphics software and media players.
Application software is contrasted with system software and middleware, which manage and integrate a computer's capabilities, but typically do not directly apply them in the performance of tasks that benefit the user. A simple, if imperfect analogy in the world of hardware would be the relationship of an electric light bulb (an application) to an electric power generation plant (a system). The power plant merely generates electricity, not itself of any real use until harnessed to an application like the electric light that performs a service that benefits the user.
So I'd say a Web application is any website that allows a user to accomplish specific tasks. A website that is not a Web application is a website meant to give the user information (blogs, news, tutorials, etc.).
I would say simply that:
A web app:
- is interacted with, more than just reading pages
- can allow the user to create content
- often requires logging in
For example, forums, social networks, and all apps designed to replace desktop applications.
A website that is not a web app:
- is designed simply for reading content
For example, many small business websites, most of the standard sites you see selling ebooks with the massively long pages and never-ending 'discounts'.
Topic of debate: is a blog a web app? I would probably argue that it is, if the users often interact through comments, etc, but it might be more like a web site if there is minimal user interaction other than content consumption.
One of the best litmus tests I've seen for web app vs. web site comes from the scope discussion at Software recommendations:
If you are unsure about your question being about a website (rather then a webapp) ask yourself: "Given I had the program I'm looking for and the means to run it, but not any of the data it contains, would it still be useful?" If the answer is yes, then go ahead and ask. If the answer is no then you are looking for a data collection and this is not what this site is about.