The term Ajax is used to describe a set of technologies that enable browsers to provide users with a more natural browsing experience. Before Ajax appeared, websites forced users to enter the submit/wait/redisplay paradigm, and users' actions were always synchronized with the "thinking time" of the server. Ajax provides the ability to communicate asynchronously with the server, thus freeing users from the cycle of request/response. With the help of Ajax, you can use JavaScript and DHTML to update the UI immediately when the user clicks the button, and send an asynchronous request to the server to update or query the database. When the request returns, you can use JavaScript and CSS to update the UI accordingly, instead of refreshing the whole page. Most importantly, users don't even know that the browser is communicating with the server: the website seems to respond immediately.