Ajax, shorthand for Asynchronous JavaScript and XML, is a website design and  development technique for creating interactive web applications. The intent is to make website pages feel more responsive by exchanging small amounts of data with the server behind the scenes, so that the entire web page does not have to be reloaded each time the user makes a change. This is meant to increase the web page's interactivity, speed, and usability.

The Ajax technique uses a combination of:

• XHTML (or HTML) and CSS, for marking up and styling information.
• The DOM accessed with a client-side scripting language, especially ECMAScript implementations such as JavaScript and JScript, to dynamically display and interact with the information presented.
• The XMLHttpRequest object is used to exchange data asynchronously with the web server. In some Ajax frameworks and in certain situations, an IFrame object is used instead of the XMLHttpRequest object to exchange data with the web server, and in other implementations, dynamically added <script> tags may be used.
• XML is sometimes used as the format for transferring data between the server and client, although any format will work, including preformatted HTML, plain text, JSON and even EBML. These files may be created dynamically by some form of server-side scripting.

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

The deployment of business applications has historically forced solution developers to choose between two, often less than optimal, models: "thick" desktop installed applications, or "thin" Web browser-accessible applications. Thick applications are great for their robust features, speed and performance, but are expensive to install and deploy. Because of that, businesses today prefer Web-accessible applications. However, the functionalities are limited because HTML and HTTP were created for marking up documents and forms - not for authoring and deploying software solutions.

With Ajax, enterprises get the best of both worlds: the low cost of ownership of Website applications and the rich graphical user interface features, speed and performance of thick clients. New interfaces leverages the asynchronous communications, javascript, XML and DHTML ("Ajax") capabilities present in the ubiquitous Web browser so that you can deliver rich internet applications with no applets, plug-ins or installation of client/server frameworks. The Wall Street Journal recently noted that Ajax represents "a big step toward the Holy Grail of having the kinds of speed and responsiveness in Website based programs that's usually associated with desktop software."