AJAX uses a bit of javascript that uses the XmlHTTP object. This object, opens up a connection to a Web server, transmits and receives data, then calls back the javascript on the page which was used to invoke it.

What this means is that changes on the client side can communicate with the server, then dynamically update the client user interface without having to request a new Web page from the server.

While this slightly complicates developing Web applications that use AJAX technologies (which, by the way, is just a name given to the various technologies employed to use this methodology), it makes for a very smooth user experience since they are not constantly refreshing Web pages.

AJAX applications give an appearance of a 'thick client' application while still being a 'thin client' (i.e. application that runs in a Web browser.) However, it is important to note that network communication is still going on in the background while the application is being used.

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