AJAX is a group of interrelated web development methods used on the client-side to create interactive web applications. Web applications based on AJAX can communicate with server asynchronously, in the background without interfering with the display and behavior of the existing page. Data is usually retrieved using the XMLHttpRequest object. AJAX is a group of technologies.
For example AJAX uses combination between HTML and CSS to mark up and style information. The user can interact with presented information based on DOM which is accessed dynamically with JavaScript. The full page reloads are avoided, because XMLHttpRequest object and JavaScript provide method a method for exchanging data asynchronously between browser and server.