“Asynchronous JavaScript and XML” :

Development technique enabling a web page to process HTTP requests asynchronously , that is , without having to reload it .

As the name suggests , It relies on two languages ; Javascript and XML , a data format language .

Nowadays, developers favor the combination “Javascript + JSON format”  .

You can implement Ajax  using the XMLHttpRequest object

or the JQuery library , via its method JQuery.ajax() , aka $.ajax() .

The first method allows you to use Ajax on modern browsers even if JQuery ( or Javascript ) is disabled .

Which is not the case of the second , although the simplest .