In computer programs, operations are ‘asynchronous’ if they operate independently of other processes. This is why the web page doesn’t have to be reloaded in order to send information to the server. The exact method for this uses something called an XMLHttpRequest object, which is effectively an interface that allows scripts to perform AJAX requests.
AJAX is not just one technology. All of these technologies work together to create a single HTTP or HTTPS request. According to Jesse James Garrett, who first coined the term, the following technologies are incorporated:
- Document Object Model
- XMLHttpRequest Object
In WordPress, AJAX can be seen in action in the post edit screen where you can add a new category while writing a post without reloading the page. Another example can be seen on the comments page where you can approve or delete a comment without reloading the page.