A website and a web application have blurred lines. Each one is mistaken for the other. A website exists to show static content. A website shows static or dynamic data that is predominantly sent from the server to the user only, whereas a web application serves dynamic data with full two way interaction. A website shows essentially the same data.
In computing, a web application or web app is a client–servercomputer program that the client (including the user interface and client-side logic) runs in a web browser. [Ref. 1]
The user interface of a web application is also usually much more complicated than the user interface of a website. Websites might have tags and categories that you need to understand, but you don’t have to go through and learn any potentially complicated tasks in order to use websites. Web applications often require step-by-step guides, or you’re not going to be able to complete them. [Ref. 2]
References:
CoalWorks Official Blog 