Although Ajax can refer to a brand of cleaning powder or a mythological hero from ancient Greece, in WordPress, Ajax (sometimes spelled AJAX to differentiate it) is a special type of programming script.
If you’re only interested in administering a WordPress website, then you won’t have to worry about what Ajax is or what it does. For developers, however, Ajax is essential for writing scripts, particularly for web applications.
You can see Ajax in action in WordPress when creating a new post. If you decide to create a new category and use it with that post, you can do so without having to reload the entire page. The data that is being exchanged in order to make this update happen is powered by Ajax.
Ajax can also be added to plugins. For much more information on this and how to code Ajax, visit the WordPress website.