Web application is an application or app that could be accessed over Internet or within a system. Even a simplest web application like e-mail needs a browser to access it. web application can also be added to an already created web page using java script (AJAX). Common example for web application is Google Docs which is a free online office application.

Main things required for functioning of a web application
Browser on client side is necessary to access a web application. The Main web application content could be created using some of the application tools like ASP .NET, Ajax, PHP and Web toolkit. The must also be a database storage tools like MySql, Oracle and MS SQL server to store the data.
Web application needs a server for better functioning
Server required for storage of web application is application server. Some of the free application servers are Appaserver which colud be used for creating multiuser and database applications. Base4 which is similar to WinFS. Zope developed using Python.
The advantages of using application servers are that it is easy to update, advanced security, cost-effective and Better performance.
Business Application Providers
Web application development companies offer basic web applications to more advanced applications known as application service providers.
Why application service providers are necessary?

• Software upgrade and hardware upgrade is not necessary.
• It reduces working cost than purchasing software licenses for each computers.
• It is easy to integrate data from other applications and also between the users.

Advantages of Using Web Applications

• No need of any hardware upgrade or free disk space to run the application.
• The application automatically gets updated.
• Can be accessed from anywhere in the world at any time .
• Can be easily synchronized with several devices.

Disadvantages of Using Web Applications

• Need Internet connection to work.
• Less features when compared to desktop applications.
• Hard to develop and needs constant update to meet browser compatibility.