What is a web application?

A web application is a dynamic view of an application in a web server or application server.
They are mainly two types
Presentation-oriented:

A presentation-oriented web application generates interactive web pages containing various types of markup language (HTML, XHTML, XML, and so on) and dynamic content in response to requests. This can be achieved by technologies such as JSF, Servlet, JSP, Spring etc.

Service-oriented:

A service-oriented web application implements the endpoint of a web service. These are often consumed by the above said application. This can be achieved mainly with the help of Webservice technologies. 

A web application consists of web components; static resource files, such as images and cascading style sheets (CSS), Code that generates dynamic content such as servlet and Java classes etc. 

The process for a java web application creation can be summarized as follows:

1.    Develop the web component code.
2.    Develop the web application deployment descriptor, if necessary.
3.    Compile the web application components and helper classes referenced by the components.
4.    Optionally, package the application into a deployable unit such as war
5.    Deploy the application into a web container.
6.    Access a URL that references the web application.