AJAX stands for Asynchronous JavaScript and XML. It is not a protocol in and of itself, but is rather a mixture of technologies that includes HTML and JavaScript. This mixture of technologies represents a major paradigm shift away from the traditional approach where a person sitting in front of a desktop PC opens their browser and makes a request of a website, which in turn delivers static HTML content.
Here is a diagram of the traditional request-response sequence:
AJAX, on the other hand, turns the tables on the traditional request-response sequence illustrated in the preceding diagram. Instead, what happens is that the initial request delivers HTML content, including one or more JavaScript applications. The JavaScript applications run locally on the person's browser or smart device. From that point on, in most cases, it is the JavaScript applications that make small-scale asynchronous requests in the background.
Here is a diagram of an AJAX...
