AJAX, short for Asynchronous JavaScript and XML, is a set of web development techniques that allows web applications to communicate with a server asynchronously, without reloading the whole page. It uses a combination of HTML/CSS, JavaScript, and XML or JSON to send and retrieve data from the server. This technique enables smoother, faster, and more dynamic web experiences, as only parts of a webpage need to be updated rather than reloading entire pages. AJAX is commonly used in forms, searches, and interactive features on websites, enhancing the user experience by reducing wait times and increasing the application's responsiveness.