Web Application is about technology going to be used, and communication between them
- Client(Android/IOS(java/objective C, or some framework like, trigger io or titanium)).
- Client(Browser app(some technologies, like css3, lesscss, jquery, or angular js)
- Web server(we have 2 servers, for example front-end server like ngnix, and back-end server like node.js or netty)
- Database server (we use 2 databases for example, mysql and couch db) I also write for which reason what you are using.