To understand AJAX, first we must know how the traditional web application works. The classic web interface trigger an HTTP request back to web server. The server then process and retrieve data before returning an HTML page to the users. This process as a model for hypertext medium makes technical sense. But as web application evolves this process does not make the user interface more interactive and practical.
AJAX, on the other hand, eliminates this problem. AJAX speed up the loading of any web application with the use of intermediate between the user and the server called AJAX engine. This adding of another layer application of eliminates the start-stop-start-stop nature on the web. The browser loads an AJAX engine at the start of session.
The AJAX engine allows the user interface and the application to interchange data asynchronously-independent of the communication to the server. So the interaction between the user and the web never slows down, no point of waiting for the server to do something.
AJAX is a powerful technique that grows exceptionally as web application. That is, AJAX is now part of the guiding principle as web 2.0 flourishes and becomes a practical reality. With the power of AJAX, many of the business and marketing web site are integrated with AJAX application server platform now. Most of the major products of Google such as Gmail, Google Maps, and Google Suggest are employing AJAX application. Other web services like the photo-sharing application Flickr, Amazon's A9.com, and the new Yahoo! maps depends on AJAX. The application of AJAX comes from simple function to the most complex program like Google Maps.