A web application is any application that uses a web browser as a client. The application can be as simple as a message board or a guest sign-in book on a website, or as complex as a full database system used to run a large company.

What is a Client?

The ‘client’ is used in client-server environment to refer to the program the person uses to run the application. A client-server environment is one in which multiple computers share information such as entering information into a database. The ‘client’ is the application used to enter the information, and the ‘server’ is the application used to store the information.

What are the Benefits of a Web Application?

A web application relieves the developer of the responsibility of building a client for a specific type of computer or a specific operating system. Since the client runs in a web browser, the user could be using a PC or a Mac. They can be running Windows 98, Windows XP or Windows Vista. They can even be using Internet Explorer or Firefox.
Web applications commonly use a combination of server-side script (ASP, PHP, etc) and client-side script (HTML, Javascript, etc.) to develop the application. The client-side script deals with the presentation of the information while the server-side script deals with all the hard stuff like storing and retrieving the information.