AJAX, Asynchronous Javascript and XML, is a collection of web development techniques that enables a web page to interact with a server without reloading the page. AJAX allows web applications to share data with the server without messing with the current web page. Although the “X” is meant to stand for XML, it is not required to use XML for data exchange. Instead, JSON can be used.

Asynchronous operations in computer programs are those that run independently of other processes. This is why the web page does not need to be reloaded to send data to the server.

The precise method for this makes use of an XMLHttpRequest object, which is basically an interface that allows scripts to perform AJAX requests.

AJAX is more than one technology. All of these technologies collaborate to generate a single HTTP or HTTPS request. The following technologies are integrated, according to Jesse James Garrett, who coined the term:

Document Object Model
XMLHttpRequest Object

AJAX can be seen in action in WordPress in the post edit screen, where you can add a new category when writing a post without having to reload the page. Another example is the comments tab, where you can accept or remove a message.