AJAX is an acronym for Asynchronous JavaScript and XML. This technology speeds up operations on a page by avoiding the need to reload the page to perform a chosen action.
It works by sending data to the server in the background. Only a certain part of the page then changes, so the whole HTML page does not have to be loaded again.
For example: when a user clicks a button to vote in a poll, the whole page would have to be reloaded from the server, even though only the poll results are updated and all the rest of the content stays the same. With AJAX, the user's vote is sent in the background, the server returns only the parts of the page that changed, and only those parts are updated and redrawn on the page.
Uses:
AJAX became important mainly thanks to Google, which started using it in its applications (Gmail, Google Maps, Google Docs and others). In practice, it can be applied to things like search suggestions, online maps, discussion forums, filters or pagination in online shops, and other applications.
Advantages and disadvantages
One major disadvantage of this technology is that it requires a modern web browser with full support for JavaScript.
Without AJAX, the whole page would reload and flicker every time you click a link, and you would have to wait for it to load. With AJAX, you most likely will not even notice that the page has been updated and that, for example, the address has changed.