AJAX (Asynchronous JavaScript and XML) is an umbrella term for a collection of Web development technologies used to create interactive Web applications, mostly W3C standards (the XMLHttpRequest specification is developed by WHATWG):

1) XHTML - a stricter, cleaner rendering of HTML into XML

2) CSS for marking up and adding styles.

3) The Javascript Document Object Model (DOM) which allows the content, structure and style of a document to be dynamically accessed and updated.

4) The XMLHttpRequest object which exchanges data asynchronously with the Web server reducing the need to continually fetch resources from the server.

Since data can be sent and retrieved without requiring the user to reload an entire Web page, small amounts of data can be transferred as and when required. Moreover, page elements can be dynamically refreshed at any level of granularity to reflect this. An AJAX application performs in a similar way to local applications residing on a user's machine, resulting in a user experience that may differ from traditional Web browsing.