Ajax - Asynchronous JavaScript and XML is the paradigm to create dynamic websites and more efficient.
Let us explore it, In older days when you want load options in a Select  or combo box based on first
select control value you have to reload the page or redirect to false page. Now what Ajax will do in the
same situation It will load options or values in the second select control based on first select without
redirecting and reloading the web page.

How it is possible?

There will be a redirect and response but the page you viewing doesn't show anything. Ajax script
which is a combination of JavaScript and XML will run between your HTML page and server script
like PHP or ASP..Ajax script send client request to server script and receive the response from server
script. Backend server script will be executed by Ajax script.

What is Ajax Script?

Its a single page JavaScript coding consist of http variables, XML and JavaScript methods to process
client - server request and responses.