At one point in the history of the Internet, in order for a website to communicate with a server, it had to be reloaded. This meant that if a user needed to enter data into a form, or for some reason needed to communicate data to the server, when he or she hit the input key the website would automatically reload. This could lead to an interrupted experience on the website, particularly if the user was using a slower Internet connection.
AJAX is a communication protocol that allows websites to send information to the server without the need to reload the page. AJAX techniques are “asynchronous” techniques; that is to say, they operate independently of other programs that may be running.
AJAX technologies are separate and distinct technologies or scripts that work together to fashion a single request to the server. Doing this, they allow users to interface with the server without needing to reload the page.
Examples of AJAX in use include editing and adding posts to a website without the need for reloading it. Likewise, the ability to add, review, reject, and even delete comments without reloading the page is an illustration of AJAX in action.