A WEB application is a software that the users can access through a web browser such as Chrome or Firefox. The browser MAKES an HTTP request for a specific URL for the web application. The web application server intercepts and processes the request to build a dynamic HTML response sent to the user. Some examples of popular web applications include StackOverflow, Reddit, GOOGLE, etc.

A web application is different from a typical website. A website is static. When you go to the website, it returns an HTML page without doing any processing to build the contents of that HTML page. You will see the same page if you reload the browser. In contrast, a web application might return a different response each TIME you VISIT.

For example, let’s say you ask a question on Stack Overflow. Initially, you will see only your question when you visit the URL. However, if another user answers your question, the browser will display that answer on your next visit to the same URL.

A web application consists of multiple separate layers. The typical example is a three-layered architecture made up of presentation, business, and data layers. For example, the browser (presentation) talks to the application server, which communicates to the database server to fetch the requested data.

The following figure illustrates a typical Web application architecture with standard components grouped by different areas of concern.