web Based Application means Application which running on web or can say (web browser)
Best Example of Client Server Application is Web browser and a Web Server. where your browser performing as a client. for example when you address a URL in the browser, it means that your browser is requesting a page from a Web Server and Server returns an html page to the client on its request. [ January 19, 2007: Message edited by: Saif uddin ]
I believe the main advantage of a web based application is that you do not have to write the client(browser) and you will find the client in computer and makes the application more available to users without the user need to install anything new in his/her computer.