Ajax stands for Asynchronous JavaScript and XML. It is a set of web development techniques using many web technologies on the client-side to create asynchronous web applications.
With Ajax, web applications can send and retrieve data from a server asynchronously (in the background) without interfering with the display and behavior of the existing page.
It involves making use of the XMLHttpRequest object to exchange data asynchronously with the web server. However, data returned from the server is not limited to XML, it can be in other formats such as HTML, JSON, or plain text.
This means a web page can update some parts of its content dynamically and without reloading the whole page, offering a more fluid and responsive user experience.