Asynchronous JavaScript and XML (AJAX)

Asynchronous JavaScript and XML, commonly known as AJAX, is a relatively new programming development, essentially allowing rich effects to occur as a user views a website, without needing to reload or postback the page.

Use of AJAX can often be seen in online forms, where entering information is checked for validity without the page refreshing. This is very useful, and user friendly, for checking information such as passwords, emails, and usernames against input rules.