AJAX stands for A
ML. it is a technology that enables a webpage to communicate with a file on its server without the webpage reloading or the web user noticing.
A server is a computer or device where your website lives. If your webpage or website is on your personal computer, then your PC is the server. If it is on your phone, that is also the server. All websites are hosted on a server or computer.
You can learn AJAX in our official AJAX tutorial here.