Ajax is the new buzz word floating around, but what exactly is it? Basically, it means you can send requests back to the server in the background and your web page can carry on happily doing other things – it doesn’t have to wait for a response to the request. Usually, when you click on something on a web page you have to wait for the whole page to be reloaded whilst a response is returned from the server. Not anymore with Ajax however! Using something called the XMLHttpRequest (or simply, XHR) requests can be sent to the server, and ONLY relevant portions of a web page need to be updated accordingly.
This may not sound like much but the benefits to the user are not having to wait around for the page to be constantly reloaded every time a link is clicked on, giving web pages much more of an interactive feel to them, similar to a desktop application. One of the most common examples I have seen Ajax implemented is in the backend of content management systems (CMS), where the user can set various options by dragging elements around rather than just by clicking on standard links.