The document discusses Asynchronous JavaScript and XML (AJAX) which uses a combination of technologies like HTML, CSS, JavaScript, DOM, and XMLHttpRequest to retrieve data from the server asynchronously in the background without interfering with the display and behavior of the existing page. It provides an overview of the traditional web application model vs the AJAX model and discusses some pros and cons of using AJAX including how it can increase usability and save bandwidth but may break back button support or have cross browser issues.