AJAX (Asynchronous JavaScript and XML), or Ajax, is a group of inter-related web development techniques used for creating interactive web applications. A primary characteristic is the increase in responsiveness and interactiveness of web pages, when a user makes a small change the request can be done “behind the scenes” where the whole page does not have to be reloaded each time.

AJAX is asynchronous in that extra data is requested from the server and loaded in the background without interfering with the display and behaviour of the existing page. JavaScript is the scripting language in which AJAX function calls are usually made. Data is retrieved using the XMLHttpRequest (or equivalent) object that is available to scripting languages run in modern browsers. There is, however, no requirement that the asynchronous content be formatted in XML.

AJAX is a cross-platform technique usable on many different operating systems, computer architectures, and web browsers as it is based on open standards such as JavaScript and the DOM.

Like DHTML, LAMP, and Ajax is not a technology in itself, but a term that refers to the use of a group of technologies.

The "core" and defining element of Ajax is the XMLHttpRequest object, which gives browsers the ability to make dynamic and asynchronous data requests without having to reload a page, eliminating the need for page refreshes.

Besides XMLHttpRequest, the use of DOM, CSS, and JavaScript provides a more-enhanced "single-page" experience.

The core jusThe core justification for Ajax style programming is to overcome the page loading requirements of HTML/HTTP-mediated web pages. Ajax creates the necessary initial conditions for the evolution of complex, intuitive, dynamic, data-centric user interfaces in web pages—the realization of that goal is still a work in progress.

Some uses for Ajax interactions are the following

• Real-time form data validation: Like validation of email addresses, without having to go to the server to check if valid
• Auto completion: a specific portion of form data such as an email address, name, or city name may be auto completed as the user types.
• Load on demand: an HTML page can fetch more data in the background, allowing the browser to load pages more quickly
• Sophisticated user interface controls and effects
• Partial submit: An HTML page can submit form data as needed without requiring a full page refresh.